Add method of listing channel id's the bridge sees

[vranki]

When using the bridge solely for relaying using a bot, there is no way of bridging rooms via the bridge as that requires discord channel id's. Bot (probably) can see all channels in guilds it's in, so it could have a command of channels and their id's in those guilds.

Either add the channel list in "guilds status" command or add a separate command for it.

[snex]

Should be able to get all users in a discord as well. As it stands, I can only @ somebody once they've already spoken.