Improve max_age_expected help text

Text for max_age_expected made more 'business person friendly'

https://www.pivotaltracker.com/story/show/70376934

[Delivers #70376934]
Automatically run migrations in development

So that when someone does `bowl stagecraft` for the first time, they
automatically get a database (albeit a totally empty one).

https://www.pivotaltracker.com/story/show/68997642

[#68997642]
Use X-Forwarded-Proto to determine is_secure

Use the X-Forwarded-Proto header to determine whether the request is
secure or not. This allows Stagecraft to correctly generate URLs to
itself.

https://docs.djangoproject.com/en/1.5/ref/settings/#secure-proxy-ssl-header
Merge pull request #129 from alphagov/use-forwarded-proto

Use X-Forwarded-Proto to determine is_secure
Merge pull request #130 from alphagov/improve-max-age-expected-help-text

Improve max_age_expected help text
Merge pull request #131 from alphagov/auto-run-migrations-in-dev

Automatically run migrations in development
Improvements to auto_ids help text

Changing the text to make problems like #70178060 less likely to occur in future.

https://www.pivotaltracker.com/story/show/71033154

[Delivers #71033154]
Merge pull request #132 from alphagov/improve-auto-ids-help-text

Improvements to auto_ids help text
Improve error messages shown from Backdrop

- Handle previously uncaught `ConnectionError`
- Make 4 new subclasses of Backdrop error:
  - BackdropAuthenticationError
  - BackdropConnectionError
  - BackdropBadRequestError
  - BackdropUnknownError
- Factor out the function which sends & handles errors so it's common
  between create & delete requests.
- Extract and use the error message from the Backdrop response JSON if
  available.

https://www.pivotaltracker.com/story/show/65645322

[Delivers #65645322]
Merge pull request #133 from alphagov/improve-backdrop-error-messages

Improve error messages shown from Backdrop
Add initial skeleton outline of backdrop_users (or dataset_users?)

- Adds a many2many relation with data_sets and an email field
- Also adds very basic view of users in the admin app, but that doesn't work yet
Working admin and test for unique email
wowee zowee it's a check_disabled decorator!
email not name
Add serialization to backdrop user model

- Roughly copies the serialize method on data_set model
Add the fixtures we were actually using back into data_set view test
Add url route for user lookup

- new matcher based on looking up by email in url
- implies a split in views in the import
Add in test data and view tests for backdrop user views
Stricter ignoring of log files in .gitignore
Remove debug printing