Simplify OAuth2 for outlook.office365.com server

With these changes I'm able to connect to the office365 instance at $work, where additional restrictions seem to be enabled. None of this comes from "insider" knowledge, merely from observing how davmail works: https://github.com/mguessan/davmail/blob/master/src/java/davmail/exchange/auth/O365InteractiveAuthenticator.java#L94