Hmmm, this turned out to be a monster commit.  This change allows the
basket to be able to correctly calculate prices including tax.

It also requires a whole load of test changes since all baskets now
require a strategy instance to be assigned.

* Emailbackend: Updated to use REQUIRED_FIELDS
* Demo and sandbox site now use compat.AUTH_USER_MODEL as well
* Added example custom user that gets tested for Django >= 1.5

The auth backend now gracefully handles situations where there are users
with the same email address.

* Doesn't use progressive plugin on travis (which made the console
  output unreadable).
* Allows arbitrary nose options to be used with ./runtests.py.  Before,
  they might get clobbered.
* Avoid dupliation issue with nose picking up options independentally
  from the testrunner script

Default behaviour is still the same.

This is much faster than the default and cuts around 20 seconds off the
runtme for the test suite.

I forgot to modify the test config to account for django-compressor.

Distinguish it from the other folders which each define a category of
test.

* New attribute on product class
* Optimised checkout for digital goods

This is needed for internal Tangent projects.  The search app in oscar
still needs some work but it works in a very basic fashion at the
moment.

The template for search results still needs attention.

This avoids conflicts with other libraries that use the same trick for
extending templates.

Plus tweaks to test method names

Also split them into unit and functional tests.

- Tidied up JS slightly, using 4 space indentation
- Moved layout_* templates into folders
- Few updates to the base templates
- Put oscar's JS into its own folder within static/js
- Added flatpages to the test env to get tests to pass