Drop django-auth-ldap configuration we're not going to use

Add more values to USER_OBJECTCLASS, introduce DEV_OBJECTCLASS for future use
Add django-ldapdb in settings and dependency list

django-ldapdb is a library that uses LDAP server as Database backend.
This way we will be able to use ORM by mapping LDAP users to python objects
trivial change
whitespace
sync tests/settings with okupy/settings/*
Move tests.tests.example_directory to tests.settings.DIRECTORY
Add LDAPUser model, from django-ldapdb

It is in very early stage, plus it has many hardcoded things, but it provides
the API we want to get LDAP accounts as python objects.

TODO list regarding LDAPUser and django-ldapdb can be found at:
https://github.com/gentoo/identity.gentoo.org/wiki/TODO_tampakrap#django-ldapdb

Example:
>>> alice = LDAPUser.objects.get(username='alice')
>>> developers = LDAPUser.objects.filter(ACL__contains='dev.group')

PS Since it is in early stage, and the final form of it is not fully defined
yet, I'm skipping the tests for now till we have a final design
comment django-ldapdb configuration in tests.settings because:

1) they are not used yet
2) they are breaking ALL the existing tests, needs to be fixed ASAP
The error is:
TransactionManagementError: Transaction managed block ended with pending COMMIT/ROLLBACK
minor improvement in settings.DIRECTORY, upgrade alice to developer
switch to our fork of django-ldapdb
Add TLS and CONNECTION_OPTIONS for ldapdb
Add object_class field to retrieve objectClass LDAP attribute

Please note that object_class is NOT the same as object_classes
object_class retrieves the objectClass LDAP attribute for a user,
while object_classes is a variable that has all the available object classes
which is used internally by django-ldapdb for various operations eg search,
creation of new object etc
Merge pull request #24 from tampakrap/ldapdb

use django-ldapdb