Video camera: add audio inputs and outputs independent of audioEncodingTarget

Add -(BOOL)addAudioInputsAndOutputs and -(BOOL)removeAudioInputsAndOutputs to GPUImageVideoCamera to manage audio inputs independent of setting audioEncodingTarget.

Previously, if you add or change the audioEncodingTarget, the inputs are recreated, which triggers a pause in the app.

Also I added a being/commit configuration around removing the audio & video inputs and outputs. Also I added nilling those inputs, to match the old removing of audio inputs behaviour.