Fixed LIB robot user/cert migration.

Added guardian migration for LIB user pipeline perms.

Corrected LIB username.

Fixed translator.py to read JSON for LIB events.

Needed to freeze gracedb for guardian migration.

Changes for new LIB user/pipeline and permissions.

Added model level permissions on Guardian.GroupObjectPermissions for members of the executives group. Also restored a modified version of the ModelBackend that *doesn't* do authentication. This is so that the has_perm check on Models can work.

Added changes to ligoauth.middleware.auth to allow user creation in the event that the user is not already found in the database. Applies to shib only.

Added context processor for login URL, added login URL to base template, added embedded discovery service page.

Added public url patterns in ligoauth/middlware/auth.py. Note: This is a temporary hack to facilitate registration with InCommon.

Fixed bug due to Django 1.6 update. The get_or_create call in refresh_users_from_ldap.py needed some default arguments. Otherwise, it tries to create a user with an empty username, and that will collide with another user with an empty filename and cause an unhandled exception.

Added Bayestar MIC robot DN and user. This is a temporary robot for ER5. Should probably be removed when Leo doesn't need it anymore.

Added migrations for gdb_pe robot cert and 'background' tag. Also added 'background' to the list of blessed tags in the settings module.

I (Branson) found this local change to refresh_users_from_ldap on archie. It looks harmless, so I'm keeping it.

https://bugs.ligo.org/redmine/issues/732