src/WebRTC: make `mediaHint` always be an object literal

Remove irrelevant/bad tests

fixes #34
src/WebRTC/MediaStreamManager.js: object keys have to be Strings

See https://github.com/onsip/SIP.js/pull/44#commitcomment-6755635

Note: I x'ed a test that I couldn't get to pass, even though the code works in practice.
 #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
 #33 DataChannel support - first cut

 - mediaHint.dataChannel
 - WebRTC.MediaHandler.on('dataChannel', function (dc) {});
 - WebRTC.MediaHandler.dataChannel

 See https://github.com/wakamoleguy/SIP.js/commit/78398294f9b05626baebc22e130ae23709a1c6a3
 #35 Provide <audio> or <video> elements to MediaHandler - first cut

 Usage:

  var session = new SIP.UA().invite('welcome@junctionnetworks.com', {
    media: {
      render: {
        remote: {
          audio: document.createElement('audio'),
          video: document.createElement('video')
        },
        local: {
          audio: document.createElement('audio'),
          video: document.createElement('video')
        }
      }
    }
  });
Merge pull request #44 from joseph-onsip/34

src/WebRTC: make `mediaHint` always be an object literal