#23 Media Events: squashed commits:

  - [23] MediaStreamManager events (#23)

  - [23] MediaHandler events - first cut #23

  - #23 Media event tests - expect spy calls instead of checking flags

  - #23 MediaStreamManager events - dedupe getUserMedia callback wrappers

  Also, fix the test mentioned in https://github.com/onsip/SIP.js/pull/44#issuecomment-46779699