GPUImageVideoCamera: Add -(BOOL)addAudioInputsAndOutputs and -(BOOL)removeAudioInputsAndOutputs to manage audio inputs independent of audioEncodingTarget

Previously if you add or change the audioEncodingTarget the inputs are recreated, which triggers a pause in the app.
GPUImageVideoCamera: begin & commit configuration when removing inputs and outputs
GPUImageVideoCamera: nil ivars are removing inputs and outputs
Merge pull request #1167 from karlvr/video-add-audio-inputs-and-outputs

Video camera: add audio inputs and outputs independent of audioEncodingTarget