further simplify our in-app settings implementation and solve the remaining issue with the subtitle encoding setting (close #8679)

Switch settings implementation to a saner approach, so the user can set most options both in System Settings and in-app (using InAppSettingsKit)

TODO: re-add l10n support, fix in-app setting of subtitles text encoding (only supported in System Settings right now)

Add InAppSettingsKit to xcodeproj and compile it with disabled ARC to avoid patches against upstream

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)