Small refactorings & improvements

* "crypt" core service is renamed to "crypto"
* ActionsManager Plugins behaviour refactoring + small security improvement
Added "priorities" to Actions, added a small security check for PluginsManager

* Actions defined in Plugins config files can now have a "priority" property; Actions with higher priorities have precedende over others. That way, an Action can "override" another Action.
* PluginsManager's "include file in Closure" function now checks that the request file is in the project directory, and throws an Exception if something nasty is detected
Added a first draft of the "Forums display" homepage

* our Forum model class now have a "parent/children" logic, and we have a "$app['forum.forums-data.tree']" Service wich gives us a complete tree of our Forums
* the "forum-base" Plugin overrides the default "core" homepage with a Forums display
* added some basic styling on this page with our default Twitter Bootstrap "poor man's theme"
* phpBb Forums import update: the forums name and description are now "HTML-escaped"