Adds a new button to Roundcube's mailbox toolbar to mark the selected
messages as Junk/Not Junk, optionally detaching original messages from
spam reports if the message is not junk and learning junk/not junk using
various methods (sa-learn, etc.).

Warning: this plugin is unmaintained and may be removed in the future.
Users should migrate to the "markasjunk" plugin in the main Roundcube package.
