Make ImapHelper constructor throw

Instead of checking with isSuccessfullyInitialized(), ImapHelper now
throws an checked InitializingException if it cannot be initialized.

+ Recategorize VVM3 error for non-IMAP errors.

Change-Id: Ifd17f154b580efdc09535d8a7751b0031326d92c
Fixes: 30032461
Fixes: 30106330
6 files changed