fixing default configuration

better configuration example

adding descriptions for roles

simplify roles configuration (backend groups)

unit test + admin roles fix ...

* adding various unit tests
* now admin roles are inherited (ex admin-lv2 is admin -> admin-lv3 is admin
* adding an exception when requesting groups for none existant role

implementing nesting roles

correcting identation on roles.yml configuration file

adding a canevas for role definition