Themes: Add method to "apply all" a theme

Change-Id: Ic8feaeade6c52707e6b5b17921b1b577b94ec8cf
Themes: Add URI for querying previews of applied components.

Change-Id: I97417901f3b03fc82df5a823970991ddd8092df2
WallpaperCropper: load wallpapers in the background

Change-Id: I134d94a85f25bf5db4c15fa9a89265c53e5b0c1d
Signed-off-by: Roman Birg <roman@cyngn.com>