gui: Allow automatic device ID selection on WebKit browsers (ref #8544) (#8597)

Some WebKit browsers select more than needed when using double click to
select device IDs, e.g. new lines and white space. This commit adds a
prefixed version of user-select in CSS in order to add support for those
browsers and allow them to select just device IDs automatically.

Signed-off-by: Tomasz Wilczyński <twilczynski@naver.com>

gui/default/assets/css/overrides.css

@@ -550,5 +550,6 @@ html[lang|="ko"] i {
 }
 
 .select-on-click {
+    -webkit-user-select: all;
     user-select: all;
 }