fix self user password modification in AD Backend ...

In some forms, the 'cn' attribute might not be accessible.
The _set_password method relied on 'cn' to build the user dn.
Now it accepts the cn or the dn (by_cn switch).

Fix encoding issues in AD backend

pepify the source code

making some attributes explicitly mandatory for Active Directory backend

fix password setting with Active Directory

multiple modification/fix ...

* add display_name parameter for backend
* handle display_name in modify template (lonely groups) and error
  message
* fix bug in modify when user is in only one backend
* remove redondant exception in ad/ldap backend
* fix unit test accordingly
* fix License in AD backend (GPLv3 -> MIT, previously tought of using
  samba4 python library which is GPL, but this module finaly uses
  python-ldap which is MIT compatible)

fix authentification for AD backend

many fixes in encoding handling

removing utf-8 crap in AD backend ...

the crap must be fixed in LDAP backend first

fix pep8 compliance

typo + add/del group in AD backend ...

* implementing add_to_group and del_from_group in AD backend.
* fixing typo self.objetclasses => self.objectclasses

fix recovery of groups in AD backend

adding filter for ad backend

fix search template for AD backend

fix unit tests

renaming and begining implementing the ad backend