[ios] - add support for libdvdcss

This adds support for using libdvdcss on ios - it allows playback of encrypted iso files.

Its based on a patch mentioned here:

http://forum.kodi.tv/showthread.php?tid=113944&pid=928429#pid928429

Not really sure if we need it (wasn't requested by anyone yet) - but i just didn't want to loose the code. I verified it with an unencrypted ios only so far (it uses libdvdcss for read - startup time is a bit slower because libdvdcss checks each vob file prior playback).

More an RFC and definitly for after Helix.