Misc Plugins Packing bugfixes & optimizations

* All Plugins Packing code is now is the PluginsPacker
* Added a setting in the app config file, allowing us to set a base URL available during the CLI compilation of the PHP Packs
* Added an array to allow app customization; the "app.php" file is no longer a black box :-)
Added "csrf" Service, misc bugfixes & optimizations

* Added the "csrf" Service and its environment (CSRF check on POST / PUT / DELETE requests, CSRF token storage in session, token usage in forms & Ajax queries...)
* bugfix on "crypto" Service
* Added Symfony "Security Core" & "Security CSRF" libraries