Mail Management UI improvement

[momo]

Yes, it works for new account. (Won't retroactively create these email).

The ticket 918 is about having the choice of not counting these email account in the limit for a user, and hide them in the list.

I will start the coding now so admin have the choice of not counting default email, and user can check "hide default" (checked by default) to hide them. Uppon uncheck, these are grey out but user can still delete these for now as a start.