Represent bridge bots in rooms differently

[turt2live]

I'm not sure what a solution would look like, however the bridge bot being an admin in the room is scary to many users. It also doesn't help with removing the integration: many think that kicking the bridge will work, but they can't because it's an admin

[turt2live]

Currently there's two common ways to set up a bridge in a room:

• Use Scalar
• Invite the bridge bot to the room and set it up manually

For both cases it might be best to hide the bridge bot from the member list and change the join event to be "TravisR added an IRC bridge to the room" or something.

This is all blocked on something like https://github.com/matrix-org/matrix-doc/issues/425