Allow matrix users to use matrix as an IRC bouncer client

This is a follow up from #2490332: Evaluate whether to replace drupal IRC channels with another communication medium.

As per comment #334. The changes being made will

1) Reallow the gateway that freenode staff has i-lined.
2) block any users with a [m] in their name. Users will have to talk to services before using a bridge.

This will result in anyone who is still attached to matrix with a [m] in their username being kicked. We are setting the kick message to include directions on how to register with services.