Allow one email account to be used in multiple rooms

[bpcurse]

A new feature could be the use of one email account in multiple rooms.

A copy of every incoming email would then have to be delivered to all participating rooms.
On setup there should be a warning like "This account is already in use, do you want to proceed anyway?"

related to #24

[JojiiOfficial]

I'll have a look how easy it would be to implement this feature. Give me a few days.