Added getSource support to the test page

Added getSource support to the test page
I'd make this a helper function called twice instead of a for-loop. 

For example I think you could add this function:
  function addSourceIdConstraint(constraints, mediaType, sourceId) {
    if (constraints[media] == true || constraints[media].optional == null)
      constraints[media].optional = {};
    constraints[media].optional.push({sourceId: sourceId}
  }

Then call
addSourceIdConstraint(constraints, 'audio', audioSelect.value);
addSourceIdConstraint(constraints, 'video', videoSelect.value);

Or something like that :) should get rid of the need for angular as well.