Movie View: be nice with the user's battery and stop video decoding when app is in background (close #8678)

there is room for improvement, as the UIPickerView is both ugly and unnecessary huge

Requires the latest MobileVLCKit to compile

remove over-engineered crop feature and reduce the number of choices for aspect ratio changes to a reasonable set (close #8670)

additionally, add a header to collect the string constants used to provide the settings within the app

http file downloader: add a proper class taking care of this and use the circular progress indicator for visualization in the popover