Added a "alerts display" Service, WIP on phpBb imports, CSRF improvements, usual CS fixes

* we now have a "utils/services/alerts-service" JS AMD module, which displays alerts translated and rendered by PHP, with all our Plugins capabilites
* added automatic CSRF token inclusion to POST, PUT & DELETE jQuery Ajax requests
* our app CSRF protection can now handle the 'X-CSRF-Token' HTTP header
* added a "finish import" step to phpBb data import, to clean heavy Session vars
* phpBb Ajax import steps are now sent via POST method, giving them automatic CSRF protection (and this is more REST-y, as these URLs do update DB data)
* misc improvements & bugfixes
* usual CS fixes hre and there