Fixes these exceptions:
```
[2019-12-22 20:48:14.779 +01:00] [ERR] Error in WaitForExit
System.InvalidOperationException: No process is associated with this object.
at System.Diagnostics.Process.EnsureState(State state)
at System.Diagnostics.Process.EnsureState(State state)
at System.Diagnostics.Process.GetWaitState()
at System.Diagnostics.Process.WaitForExitCore(Int32 milliseconds)
at System.Diagnostics.Process.WaitForExit(Int32 milliseconds)
at Emby.Server.Implementations.Diagnostics.CommonProcess.WaitForExit(Int32 timeMs) in /home/pi/dev/jellyfin/Emby.Server.Implementations/Diagnostics/CommonProcess.cs:line 100
at MediaBrowser.MediaEncoding.Encoder.MediaEncoder.StopProcess(ProcessWrapper process, Int32 waitTimeMs) in /home/pi/dev/jellyfin/MediaBrowser.MediaEncoding/Encoder/MediaEncoder.cs:line 785
[2019-12-22 20:48:14.790 +01:00] [INF] Killing ffmpeg process
[2019-12-22 20:48:14.795 +01:00] [ERR] Error killing process
System.InvalidOperationException: No process is associated with this object.
at System.Diagnostics.Process.EnsureState(State state)
at System.Diagnostics.Process.EnsureState(State state)
at System.Diagnostics.Process.Kill()
at Emby.Server.Implementations.Diagnostics.CommonProcess.Kill() in /home/pi/dev/jellyfin/Emby.Server.Implementations/Diagnostics/CommonProcess.cs:line 95
at MediaBrowser.MediaEncoding.Encoder.MediaEncoder.StopProcess(ProcessWrapper process, Int32 waitTimeMs) in /home/pi/dev/jellyfin/MediaBrowser.MediaEncoding/Encoder/MediaEncoder.cs:line 799
[2019-12-22 20:48:14.808 +01:00] [ERR] Error in "ffprobe"
System.Text.Json.JsonException: The JSON value could not be converted to System.String. Path: $.streams[0].start_pts | LineNumber: 32 | BytePositionInLine: 26.
---> System.InvalidOperationException: Cannot get the value of a token type 'Number' as a string.
at System.Text.Json.Utf8JsonReader.GetString()
at System.Text.Json.Serialization.Converters.JsonConverterString.Read(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options)
at System.Text.Json.JsonPropertyInfoNotNullable`4.OnRead(JsonTokenType tokenType, ReadStack& state, Utf8JsonReader& reader)
at System.Text.Json.JsonPropertyInfo.Read(JsonTokenType tokenType, ReadStack& state, Utf8JsonReader& reader)
at System.Text.Json.JsonSerializer.HandleValue(JsonTokenType tokenType, JsonSerializerOptions options, Utf8JsonReader& reader, ReadStack& state)
at System.Text.Json.JsonSerializer.ReadCore(JsonSerializerOptions options, Utf8JsonReader& reader, ReadStack& readStack)
--- End of inner exception stack trace ---
at System.Text.Json.ThrowHelper.ReThrowWithPath(ReadStack& readStack, Utf8JsonReader& reader, Exception ex)
at System.Text.Json.JsonSerializer.ReadCore(JsonSerializerOptions options, Utf8JsonReader& reader, ReadStack& readStack)
at System.Text.Json.JsonSerializer.ReadCore(JsonReaderState& readerState, Boolean isFinalBlock, ReadOnlySpan`1 buffer, JsonSerializerOptions options, ReadStack& readStack)
at System.Text.Json.JsonSerializer.ReadAsync[TValue](Stream utf8Json, Type returnType, JsonSerializerOptions options, CancellationToken cancellationToken)
at MediaBrowser.MediaEncoding.Encoder.MediaEncoder.GetMediaInfoInternal(String inputPath, String primaryPath, MediaProtocol protocol, Boolean extractChapters, String probeSizeArgument, Boolean isAudio, Nullable`1 videoType, Boolean forceEnableLogging, CancellationToken cancellationToken) in /home/pi/dev/jellyfin/MediaBrowser.MediaEncoding/Encoder/MediaEncoder.cs:line 399
at MediaBrowser.Providers.MediaInfo.FFProbeVideoInfo.ProbeVideo[T](T item, MetadataRefreshOptions options, CancellationToken cancellationToken) in /home/pi/dev/jellyfin/MediaBrowser.Providers/MediaInfo/FFProbeVideoInfo.cs:line 122
at MediaBrowser.Providers.Manager.MetadataService`2.RunCustomProvider(ICustomMetadataProvider`1 provider, TItemType item, String logName, MetadataRefreshOptions options, RefreshResult refreshResult, CancellationToken cancellationToken) in /home/pi/dev/jellyfin/MediaBrowser.Providers/Manager/MetadataService.cs:line 815
```
* Add support for ffmpeg 4.2
* Parse the complete ffmpeg version instead of only the first 2 digits
* Make max and min version optional
* Remove max limitation (for now)
* Style improvements
1) Reworked FFmpeg and FFprobe path discovery (CLI switch, Custom xml, system $PATH, UI update trigger). Removed FFMpeg folder from Emby.Server.Implementations. All path discovery now in MediaEncoder.
2) Always display FFmpeg path to user in Transcode page.
3) Allow user to remove a Custome FFmpeg path and return to using system $PATH (or --ffmpeg if available).
4) Remove unused code associated with 'prebuilt' FFmpeg.
5) Much improved logging during path discovery.
This makes resolving dependencies from the container much easier as
you cannot resolve with primitives parameters in a way that is any
more readable.
The aim of this commit is to change as little as possible with the end
result, loggers that were newed up for the parent object were given the same
name. Objects that used the base or app loggers, were given a new logger with
an appropriate name.
Also removed some unused dependencies.
Add Argument*Exceptions now use proper nameof operators.
Added exception messages to quite a few Argument*Exceptions.
Fixed rethorwing to be proper syntax.
Added a ton of null checkes. (This is only a start, there are about 500 places that need proper null handling)
Added some TODOs to log certain exceptions.
Fix sln again.
Fixed all AssemblyInfo's and added proper copyright (where I could find them)
We live in *current year*.
Fixed the use of braces.
Fixed a ton of properties, and made a fair amount of functions static that should be and can be static.
Made more Methods that should be static static.
You can now use static to find bad functions!
Removed unused variable. And added one more proper XML comment.
