Added interface configuration option

This adds the ability to disable the settings interface in the admin menu. This is useful because many refinerycms extensions is dependent on refinerycms-settings, but you may not want to allow your admin users to change or see the settings menu tab and interface. 

Fx. refinerycms-blog have settings for commenting and moderation that all can be configured through the blog tap, so there is no need to force the settings tap into the admin panel.