new filters for dev sprint 2

photo and video rotation using transpose: feature #130
photo and video cropping: feature #129
added simple tests for new filters
Provide convenience methods to determine mimetype
Install sox binary and start work on crossfader
sox: add trimming method to trim audio files
sox: complete trimAudio, add fadeAudio
sox: add combine and combineMix methods
sox: implement crossfader + concatenator in sox
Merge pull request #4 from abeluck/sox

Simple sox support (w/ crossfader)
update android-ffmpeg submodule
udpated to sdk 17
added photo+audio slideshow rendering
add media stream encoding back in
new features for audio crossfade and export
many updates for improved audio and slideshow rendering