Publicly advertise bridged accounts and rooms

[ludwigbald]

(part of my secret masterplan for awesome bridging and leveraging existing networks)

I want to be able to use matrix while my friends still use their IM service of choice.
I want to be able to send them a matrix.to link instead of worrying about which messenger they prefer.

For easy discovery, we need to have standard ways of doing the following:

1. Allow bridges to automatically advertise the bridged account on the identity server for [bridged] -> [mxid]
2. Allow bridges to automatically advertise the bridged account in the profile for [mxid] -> [bridged]
3. Enable matrix.to (and other messengers) to read and display public profile information.
4. Same thing goes for rooms! There should be a standardized way for rooms to advertise publicly what they're bridged to. (maybe even for non-public rooms)
5. And we probably need a room directory search on the web for people who don't yet have a matrix account, but who might want to join in on the fun through bridged channels.

[Half-Shot]

The last two point are covered MSC2346

[ludwigbald]

The closest thing I can find to the last point is http://matrix.grin.hu/rooms/
Which is pretty neat already, but could be improved by a lot!