Show common rooms with a user in MemberInfo

[matrixbot]

Created by @ matthew:matrix.org.

[aliencq]

Also it would be nice to see join time for current room, and, if possible, mxid creation time.

[ara4n]

@kegsay suggests using this as a security check of sorts when viewing invites.

[ara4n]

@dbkr: reopening this as the intention was to not just show DMs in common, but all the rooms you have in common with a user.