ofxiOSSoundPlayer as default iOS player.

- removed ofxOpenALSoundPlayer and SoundEngine.
- added ofxiOSSoundPlayer and AVSoundPlayer
- updated iOS soundPlayerExample to demonstrate how both
ofxiOSSoundPlayer and AVSoundPlayer can be used within an OF app.
ofxiOSSoundPlayer as default iOS player.

- removed ofxOpenALSoundPlayer and SoundEngine.
- added ofxiOSSoundPlayer and AVSoundPlayer
- updated iOS soundPlayerExample to demonstrate how both
ofxiOSSoundPlayer and AVSoundPlayer can be used within an OF app.
updated example with different file formats.
changed synth.m4a to synth.mp3
merged.
Merge pull request #2127 from julapy/ofxiOSSoundPlayer

ofxiOSSoundPlayer as default iOS player.