fix search display ...

* fix attritues handling, not using backend attribute name but key given
  in attributes.yml

implementing weight and normalizing each kind of attributes

implement search

adding method and unit tests to get all the attributes of one backend

adding get_attributes

better unit tests

change backend key name in attributes + methods ...

* adding get_backends
* adding get_selfattributes (attributes users can change themselves)
* adding unit tests
* rename backend-attributes -> bakends (for homogeneity with role.yml)

better checks for attributes

adding checks for mandatory elements of attributes.yml

begin attributes handling manipulation