Sync_audioMuted and _videoMuted with local mediaStream if provided

[palmtown]

This commit resolves an issue whereby when a local mediaStream is passed as an option to the answer or call functions, the existing code does not sync the enabled status. This generates an issue as if the audio or video is already muted, JsSIP initiates it as not muted. Therefore, the class state is out of sync with the mediaStream option.

[jmillan]

These should also emit the corresponding 'muted' events.