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.

Also split them into unit and functional tests.

Now they are always available within the oscar app.

This uses a few new methods in oscar.core.application.Application which
enable custom decorators to be set for given view fns.

The main use case at the moment is to make it easy to ensure that
checkout is not available to non-logged-in users when
OSCAR_ALLOW_ANON_CHECKOUT is set to False.

This is required because when subclassing an app, you still want to be
able to pick up the core oscar templates.  When they are in the app
folder, this doesn't work as that app is no longer on the INSTALLED_APP