add support for matrix -> signal power level changes

[maltee1]

make Signal role ADMINISTRATOR if power level >= 50
make Signal role DEFAULT if power level <50
bridge invite and state_default upon explicit changes

works for group creation, invites or explicit power level changes

[maltee1]

I'm catching exceptions separately for each user and the permissions. I'm thinking whether that's useful, because any exception that will occur for one of the requests will likely occur for the other requests as well. So putting a try/catch block around the entire function might make sense.