fix service unavailable template

better exceptions handling for demo backend

fix pep8

cleaner way to merge user's attributes from different backends

fix decorator handling the exceptions

slightly cleaner way to handle templates loading

pep8 compliance

small code reorganization ...

* extraction of exception decorator
* extraction of log handling

adding a demo backend

implementing custom js

fix unit test on duplicate user exception

custom error handling for UserDoesntExist, UserAlreadyExists and GroupDoesntExist

typo in comment

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)

many comment + encoding fixes

fix authentification for AD backend

more encoding error fix (on ldap auth)

more encoding fixes

fix more encoding error

fix rename in modify ...

when renaming an entry, dn must be reset to the correct value for
the modifications that come after the rename.

many fixes in encoding handling

removing utf-8 crap in AD backend ...

the crap must be fixed in LDAP backend first

fix encoding error on dn

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

making Backend skeleton a child class of object ...

this enables the use of super()

Better exception re-raising ...

re-raising the exception without specifying the exception object gives
exactly the previous exception (including the correct stacktrace)
which is nicer to have for debugging.

implementing renaming entry

fix recovery of groups in AD backend

adding filter for ad backend