Mailboxes created from within Pixelated are not compatible with Bitmask IMAP

[kalikaneko]

As discussed in Bitmask issue 8798 (https://0xacab.org/leap/bitmask-dev/issues/8798), the code in LeapMailStore._get_or_create_mailbox partially duplicates the code under the public mail api in mail.mail.Account.add_mailbox, but it's missing the part that creates an entry in the local sqlcipher db.

I'd suggest to use the public api in bitmask.mail.mail.Account for mailbox creation instead.

[FrailWords]

@kalikaneko thank you for raising this bug. We will prioritize this in our upcoming iteration.