more options for episode cache size

add 1, 2, and 5 as options for episode cache size
addresses issue #512
Pulled translations
Merge branch 'patch-3' of git://github.com/mchelen/AntennaPod into mchelen-path-3
Limit use of mp4 chapter reader to mp4 files
Fixed NullpointerException in PlayerWidgetService
Added link to modified source code
Added antennapod-subscribe:// subscription scheme