Mailapi

- sorts mailboxes by username

- Custom exception class definitions
- They are mostly self-explanatory, but here is the break down:
- AliasExists: raised when trying to create an alias that already exists in the database
- DbInitError: raised when init_db has not been called
- MailboxExists: raised when adding a mailbox that already exists in the database
- NoSuchMailbox: raised when trying to access a mailbox that does not exist in the database
- DomainExists: raised when trying to create a domain that already exists
- NoSuchDomain: raised when trying to access a domain that does not exist in the database

- bookkeeping fixes:
- populates created and modified date fields when adding a mailbox
- populates modified and lastpasswordchange fields when resetting password

- fixes issue where the all aliases were not deleted when deleting a mailbox

- mailbox search
- reset mailbox password