Mantis #4322 : Optimization Thumbnail Generation.
Merge remote-tracking branch 'remotes/origin/master' into BUG-4322-Thumbnail_Generate_is_slow_for_Picture_v4

Conflicts:
	mediaportal/Configuration/Sections/GuiThumbs.cs
	mediaportal/Core/Util/Util.cs
	mediaportal/Core/Util/VideoThumbCreator.cs
	mediaportal/WindowPlugins/GUISettings/General/GUI/GUISettingsGUI_Thumbnails.cs
Merge remote-tracking branch 'remotes/origin/BUG-4322-Thumbnail_Generate_is_slow_for_Picture_v4'