(as discussed with GingerDog on IRC yesterday).
Also renamed user to mailbox in the CLI.
- renamed model/UserHandler.php to MailboxHandler.php
- renamed scripts/shells/user.php to mailbox.php
- replaced UserHandler / user with MailboxHandler / mailbox in various files
- unrelated cleanup: deleted obsolete scripts/models-ext directory
git-svn-id: https://svn.code.sf.net/p/postfixadmin/code/trunk@1019 a1433add-5e2c-0410-b055-b7f2511e0802
