Offers are now active ON their end date

This is to make date range behaviour consistent across Oscar.
Vouchers are now active ON their end date
Trim fat from testcase

Use global instead of per-method test dates.
Split voucher testcase for better coherence
Adjust view logic to ensure end dates are treated inclusively
Fix queryset filtering for active offers
Refactor re-order view, moving logic onto Line model

This thins out the view slightly although my editor is still warning me
that it is 'too complex'.  Turns out there are quite a few things to
check when re-ordering a line.

Fixes #404.
Update nginx conf files for demo/sandbox

* Set expires=max for statics
* Add types for gzipping
Extract google analytics code into separate partials

So it can be reused on other templates when required.  Also, it makes it
easier to swap it out and use an alternative tracking urchin.

Fixes #399
Offers require a start date now

I've been convinced by Tangent's UX team that this is sensible.  The
main reason being that it makes it possible to determine when an offer
started (not necessarily the same as date_created).

Fixes #412
Add profiling middleware

These can be used to dump profile stats to the console during
development.
Make logout redirect non-permanent
Convert two redirects to use temporary codes

Don't think these two should be permanent.
Fixes test after changes in latest commit
Refer explicitly to virtualenvwrapper in docs

To avoid confusion.

Fixes #429
Patch i18n holes in account template

Fixes #425
Fix preselect_related bug

Seems to only occur on sandbox site.  Needs more investigation.
Updating sandbox also flushes sorl cache

This was causing problems with products with no uploaded images.
Flushing the cache fixed it so I'm adding it the build script to avoid
future issues.
Add file logging for sorl

This is to capture any errors that occur on sandbox/demo sites.
Improve basket admin

Make several fields readonly as it doesn't make sense to edit them
directly.  This makes the admin a little more 'dashboard-like'.