Rename local_settings to just local

The name local_settings was used when there was settings/ directory,
so I needed a way to separate settings.py from local_settings.py
The _settings suffix is useless though, we can refer this file
as settings/local
Update .gitignore as well to reflect the renamed settings/local
Merge remote-tracking branch 'tampakrap/local_settings_rename'

Conflicts:
	okupy/settings/__init__.py
Move INSTANCE_NAME to local.py

Use it in more places as well
Move AUTH_LDAP_USER_DN_TEMPLATE to settings/__init__

The variable is meant to be constructed always from
AUTH_LDAP_USER_ATTR and AUTH_LDAP_USER_BASE_DN,
and never be touched
Merge pull request #8 from tampakrap/instance_name

Move INSTANCE_NAME to local.py