Classifieds phase 1

- [x] - Backend to manage classifieds
- [x] - Filtering by specified category, status (active, inactive)
- [x] - Reviewing new classifieds
- [x] - Email notifications when new classifieds are posted, delivered to an address entered in the plugin
- [x] - Managing classifieds is included in user rights options, users with this option activated can edit classifieds, set them to inactive or delete them.
Available permissions:
 - delete
 - add - (add categories)
 - edit
 - settings - (manage settings)
 - access - (access to plugin - when unset, user cant enter plugin at all, proper message will show up)
 - activate - (activate classifieds)
 - deactivate - (deactivate classifieds)
- [x] - Remove permissions when plugin is uninstalled
- [x] - Render custom page and return message when no permission given for user
in exception listener you can check what request expects and return json with error message or nice html page with no permission information.