set ldap3 client_strategy from sync to sync-restartable; in order to avoid error 32 broken pipe caused by time out

Fix #38 calling django.contrib.staticfiles.templatetags.staticfiles.static before collectstatic raise a ValueError.

In debug bug, it actually works and do not raise an exception, but in
non-debug mode, it tries to search the staticfiles manifest for the file.
If there is no manifest because collectstatic has not been run before, this fails.

Always return authenticationDate, longTermAuthenticationRequestTokenUsed and isFromNewLogin attributes

As specified in the CAS response XML schema (see Appendix A).
Fix #37 as returned attributes are now never empty.

All exception are now in ldap3.core.exceptions, methodes for fetching
attritutes and dn are renamed.

Then using the LDAP auth backend with ``bind`` method for password check, do not try to bind
if the user dn was not found. This was causing the exception
``'NoneType' object has no attribute 'getitem'`` describe in #21

We were only sorting version string lexicographically and it would have break when
we reach version 0.10.N or 0.N.10