ofxiOSVideoPlayer API updates

- replaced getPixelsRef() with getPixels()
- replaced getTexture() with getTexturePtr()
- introduced ofPixels and removed old `unsigned char` pixel arrays.
- replaced pixel order swizzling functions with vImage methods from Accelerate framework (same as in the OSX version of AV video player)
- updated ofxiOSVideoPlayer example with the API changes.
- added Accelerate.framework to iOS template project.
ok yeah that works.
in what cases would you use `const ofPixels & getPixels() const`?
problem with this method and the `ofxiOSVideoPlayer` implantation is that the pixels only get updated when `getPixels()` is called. it is not done on every frame to save on performance.
but if `const ofPixels & getPixels() const`is used to get the pixels, then its not possible to update the pixels within a const method. so just curious how this method is supposed to be used or if `ofxiOSVideoPlayer` is implementing it wrong?