MediaElementImpl: Add implementation of stub methods

Change-Id: Id74bf1ed94837fb20d1b4128fac455ea5e1a6e17
EndpointImpl: Add implementation

Change-Id: I4ed018b6a9d05e4078b58fdec2ba220fb43bef29
FilterImpl: Add implementation

Change-Id: I450debe043b73151807e10febf8b9eb3d29ba48f
HubImpl: Add implementation

Change-Id: I8cbf7b2fc16d721ea89c05fe9b51666707542dba
Rename mixerport to hubport

Change-Id: I536180812ee33b88d2d5082bbfd3012bd5e91daf
basehub: Remove all references to mixer

Change-Id: Iea6dce4f4d87427eef907c5f1cf5b0666d2df236
HubPortImpl: Add implementation

Change-Id: Ifdeb82719adf9a188e7d5a4a588354e692c7e5cb
MediaPadImpl: Add implementation

Change-Id: If83bfa88700ca5835bacb2c051af1d1daad6c755
MediaSourceImpl, MediaSinkImpl: Add implementation

Change-Id: Ie82802e17a715c2f1d35483a318f1f316a7d2905
SessionEndpointImpl: Add implementation

Change-Id: I29bc2d300ce7fc55b2d0994bb9407d1d9ad4d895
SdpEndpointImpl: Add implementation

Change-Id: Ife0b48fc4305a91ab0d02aa0340bdf3336c90fff