DataChannel [send], streams [stop], and a few other fixes.

RTCMultiConection.streams.stop method allows you stop all streams, all
local streams, all remote streams, all audio streams, all video streams,
all screen streams, all local screen streams, all local audio streams
and so on.
-. connection.streams.stop('screen')
-. connection.streams.stop('audio')
-. connection.streams.stop('video')
-. connection.streams.stop({ remote: true, video: true, screen: true })
-. connection.streams.stop({ local: true, audio: true })

-. data-channels "send" method improved.

-. fixed: onStreamEvent.isAudio/onStreamEvent.isVideo seems NULL in
mute/unmute cases with only {audio:true} or {video:true}