Tolerate ranges of power levels for logged-in matrix users

[maltee1]

Enforcing pl 0 or 50 makes sense for signal only groups, but it's problematic once groups are mixed. Users might want more fine-grained control for platforms other than Signal, without the signal bridge interfering with that. Also, if only a single user cannot be demoted (because it has the same or higher power level as the bridge bot) the entire request will fail and no power levels will be updated. Having pl 100 in a cross-platform group you created is reasonable, but will block any Signal -> Matrix power level changes, because promoting the bridge bot to anything higher is not possible (and not necessarily desirable).

I'm not sure about a sane way of handling this, that's why I'm opening an issue. I'm thinking it would make sense to

1. enforce power levels as before for Signal puppets
2. For matrix users, don't change matrix power levels within a range, e.g. don't demote Signal DEFAULT if 0<matrix pl< 50, don't demote Signal ADMINISTRATOR. Do demote DEFAULT if matrix pl > 50 and do promote ADMINSTRATOR if matrix pl < 50.
3. Do not try to change power levels of users with the same or higher power level as the bridge bot

[maltee1]

I just started having the issue that in one room the Signal bridge bot and the Telegram bridge bot are fighting to give me power level 50 and 95, respectively. This should not happen if I created groups on both platforms myself and didn't touch my power levels on either platform. So I'll soon-ish make a pull request implementing the above changes to make the signal bridge more tolerant towards power levels of logged-in matrix users. Possibly something similar would be useful for the other bridges as well.