Plugins UI

As an Owner I'd like to have ability to add/remove/configure plugins so that I can configure/administer forum

Acceptance Criteria:

• Owner is able to see Plugins menu item in admin combo box
• On Plugins page admin can configure and disable the plugins
• Owner should be able to enter a configuration page for a particular installed plugin
• Plugins appear in the list when they are in ~/.jtalks/plugins/local (the place should be configurable via property files, but this should the default value). This is needed in order to keep plugins same when JCommune is updated to the next version.
• Plugins disappear when they are removed from plugins folder ???????

Ideally:

• Plugins should get loaded without app restarting, but that can be moved to a separate iteration
• Plugins should be uploaded via UI instead of going to server and copying them there