added celery and src folder to gitignore
[SD-714][SD-718] Modified code to do LDAP authentication.
[SD-714] / [SD-718] :
    Modified to accept username for the profile to be fetched. This is necessary while creating profile via command.
    Added documentation and
    Did some refactoring to be in-line with the functionality they are doing
[SD-715]: Created a new command to import profile from AD. Still need to add the code to parse Exceptions.
[SD-715]: Command was ignoring username
[SD-714] [SD-718] [SD-715]: Refactored ADAuth to a Class and handling the exception raised by LDAP
[SD-714] [SD-718]: Disabling the ResetPassword endpoint if Authentication via AD is enabled
[SD-714] [SD-718]: app initialization fails because of superdesk.isLDAP(). This is fixed.
[SD-716]: Fixing UserTestCase as CreateUserCommand will fail when superdesk.is_ldap returns true
[SD-716]: Did some changes so as to pass the behave tests.
[SD-668] Merge branch 'SD-668'

Conflicts:
	apps/auth/auth.py
	apps/users/__init__.py
	apps/users/users.py
	superdesk/__init__.py
[SD-714][SD-718] Fixing the merge conflict.
[SD-714][SD-718] Fixing flake8 errors.
Merge remote-tracking branch 'upstream/master'
[SD-714][SD-718] Refactor the authentication code into two different modules.
Merge remote-tracking branch 'upstream/master'
[SD-714][SD-718] Refactored the reset_password endpoint.
[SD-714][SD-718] Refactored the commands.
[SD-716] Units for create user for ldap authentication.
[SD-717] Disable auth feature when ldap authentication is active.