DEPRECATE: Ability to send arbitrary messages to all peers

[DamonOehlman]

To ensure compatibility with distributed variants of switchboard and to help manage guarantees of message delivery, we are deprecating the following functionality:

• The ability to send a broadcast commands to all other signallers connected to a room, which means that the only broadcast message type we are attempting to ensure delivery of is the /announce message.
• The ability to send random text to other participants in the room, triggering a data event on the remote signallers.

It will still be completely possible to send targeted commands to known peers through the use of to messages (i.e. signaller.to(targetId).send('/foobar')), but the future of arbitrary data is being reconsidered as part of this issue. As such it is advisable to reconsider any use that you may have made of the data event on the signaller.

After working with signaller for and building apps using both quickconnect and signaller, I have rarely used the feature (and arguably only ever abused it) so for the sake of a more solid implementation this should be removed.