Django-arcutils

- Improved help text shown for default `SECRET_KEY` local setting; since
it's a secret settings, we can't set a default, so we want to indicate
that the value shown is a suggestion. It's also quoted now for easier
copypasta.
- Added default `GOOGLE.analytics.tracking_id setting = null` stage
setting since Google Analytics isn't typically used in staging, and
being prompted for it is annoying.

Fix the default `ARC.cdn.paths` local setting and improve its docs and
examples also.

*Note: This version has a bug relating to the creation of users when CAS
authentication is used, which was fixed in 2.9.1.*

Added

- Default `MEDIA_ROOT` and `STATIC_ROOT` test settings. If these aren't
set, media and static files created during testing might end up in the
current directory, which is annoying.

Deprecated

- The use of CAS response callbacks is now deprecated. A `CASBackend` or
`CASModelBackend` subclass with an overridden `create_user` method
should be used instead. It was too confusing having multiple ways of
creating users from CAS data. `create_user` also makes it convenient
to override or set additional user attributes from subclasses.

Fixed

- Fixed how `START_TIME` setting is set in `init_settings` to keep an
`ImproperlyConfigured` exception from being raised.

Upgraded

- ldap3 1.1.2 => 1.2.2

- Added ARCTasks as a dev dependency for its release tasks.
- Upgraded django-local-settings 1.0a14 => 1.0a17. Note that for now
this means settings values can't contain embedded curly braces that
are *not* intended for interpolation.

Added

- Added `ROOT_DIR` setting for use in dev only (when `init_settings()`
is used).
- Added `START_TIME` setting (when `init_settings()` is used).
- Added more default local settings (when `init_local_settings() is
used).

Changed

- Switched to new name for PostgreSQL database back end (`postgresql`).
Projects still using Django 1.7 or earlier will need to override this
to use the old name (`postgresql_psycopg2`).
- Bumped default Bootstrap version from 3.3.5 => 3.3.6.

Fixed

- Fixed how `PACKAGE` setting is initialized when using
`init_settings()`.

- Added DRF router with "proper" trailing slash policy: list/collection
routes end with a slash; detail/member routes don't. This is nicer and
also easier to use with AngularJS $resource routes.