Updated GUI setup and settings labels
- Removed TV thumb deletion from GUI setup
- Changed language files for GUI setup (TV/Video -> Video)
- More changes of settings labels
File existence cache, deleted recordings
- deleted thumbnails are explicitly deleted in the cache
- thumbnails newly loaded from the TV server are explicitly added to the cache
- thumbnails on TV server are deleted when recording is deleted
Merge remote-tracking branch 'remotes/upstream/EXP-4060-THUMBNAIL_Remoting_Setup' into 1.3Final_ADDON3_TV_Music

Conflicts:
	mediaportal/WindowPlugins/GUIPictures/GUIPictures.cs
	mediaportal/WindowPlugins/GUISettings/General/GUI/GUISettingsGUI_Thumbnails.cs
	mediaportal/WindowPlugins/GUIVideoFiles/GUIVideoFiles.cs