fixes

fix issue related to python-ldap returning lists ...

Before, no particular treatment was done on the user attributes.
This caused some issues because python-ldap systematically returns
the attribute value as a list (even if it's mono-valuated).

Now we recover the attributes used in the group attr templates,
and we "normalize" the user attributes before using it in add_to_groups
and del_from_groups.

By normalize, we mean, transforming the list to it's unique value.
In case the attribute doesn't exist or is multi-valuated, it raises an
error.

proper exception in ldap backend ...

adding proper management of none existant user in group function
if user doesn't exist.

improve robustness if user dn attribute contains something like ,cn=

better behavior if user doesn't exist in one backend

fix many encoding errors on login and password

pepify the source code

fix password setting with Active Directory

fix error messages/logs in ldap backend

custom error handling for UserDoesntExist, UserAlreadyExists and GroupDoesntExist

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

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

fix encoding error on dn

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

escaping search string for ldap

better exception handling if user or group doesn't exist

pep8 compliance

many pep8 fixes thanks to pep8ify

remove trailing spaces

various fix on ssl/tls + tests ...

* making ssl cert check and cert no check works
* adding a test to check if the cafile does exist
* reenable and fix ssl checks on travis

better exception handling in ldap backend

fix unicode

adding logs when adding a user to a group

fix unit test and fix the way ldap connexion options are handled