Support multiple sample rates

[jmcker]

We only currently support 44,100 Hz (configured at compile time) and make some assumptions based on that.

Things to consider

• If we record a file at X Hz and then play it back at Y Hz will libsndfile resample for us?
• Switching sample rate during record or playback?
• Size of ring buffer at higher sample rates. We allocate based on duration, but 2s of space at 48kHz is 1s at 96kHz.
• Testing devices for supported sample rates and perhaps falling back to something on fail.

TODO

• Replace use of SAMPLE_RATE macro with HulaSettings::getSampleRate()
• Check all timing to ensure they account for a faster or slower sample rate
• Add Controller API for retrieving HulaAudioSettings object or changing sample rate
• Write test cases for different sample rates