add methods for class Roles + unit tests ...

* adding get_allroles (list all available roles)
* adding get_display_name (get display name of a role)
* add various unit tests

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

more complex unit test for get_roles

adding a test for get_roles

implementing nesting roles

adding an exception for failures to open role file

fix on unit tests for roles

adding test cases and reworking test env