Partially fixed sendrecv/sendonly/recvonly conflicts.

## Recent Changes?

1. If Chrome starts audio+video, then Firefox can
join it with only audio or only video or audio+video.
2. If Firefox
starts audio+video, then Chrome can join it with only audio or only
video or audio+video.

You don't need to manually set
"OfferToReceiveAudio" and/or "OfferToReceiveVideo".

## Issues?

1. If Chrome starts video-only session; and Firefox joins
with only audio. Then both fails to connect; though
sendrecv/recvonly/sendonly everything is correctly implemented.
2. New
changes affects renegotiation because new-changes are manually checking
for:

    ```javascript
    // i.e. checking only first media stream

connection.attachStreams[0].getVideoTracks();