Plugins Packers code harmonization, better Silex callbacks bridge system

* Plugins packers now use the NOWDOC format instead of HEREDOC for an easier generated PHP code writing & reading
 * Added "replace" & "camelize" methods to StringUtils
 * Added a shortcut to this method and to the PackingManager to BasePacker
 * We can now handle Silex bridged callbacks with a dash in their name, thanks to a camelization of the callbacks names