Fix access_fn in Dashbiard navigation
Update oscar/apps/dashboard/nav.py
Split up contributing guidelines

They were getting quite long. They've been split up in several
subsections. Some of them are borrowing heavily from the Django docs.
Docs: Merged content from old docs

my_model_customisations_arent_picked_up now lives in a subsection of the
recipe how_to_customise_models.

The old conventions.rst is now merged into the new coding-style.rst.

The old search.rst has been dropped as it seems outdated.
Docs: Centralise sandbox instructions

Building the sandbox was explained in multiple locations, and in
slightly different ways. The sandbox now has a separate document.
Docs: Add debugging trick for model customisations

Was posted on the mailing list.
Docs: Added documentation for tox tests
Docs: Merge tests/README.rst into docs structure
Docs: Move design decisions and dev environment

They really don't belong in /contributing.
Add new `render_product` templatetag

This looks for an overriding template for the product partial, based on
the product's UPC and product class.  This hook allows projects to
provide custom partials for changing how a product appears in browsing
views.
render_product: Docs & default paths
Use new render_product tag for product carousels
Merge pull request #601 from tangentlabs/issue/601/alternative-partials

Support alternative product partials
Move compress tags into extrascripts partial

This gives more control to subclassing projects that need to add JS
assets.
Merge branch 'master' into releases/0.5
Fix error when trying to delete empty image field
Make less work with offline compression and document it
Commit CSS again (and use it by default in sandbox)

Oscar's CSS files had been removed from source control as they are
generated from the LESS files.  They were just dupliate content
ultimately.

HOWEVER, this was causing a few problems that warrant re-committing
them.

* To browse the sandbox, you were required to install lessc (and hence
  node.js) in order for the `COMPRESS_PRECOMPILERS` setting to work.
  This was too much of an overhead as most people playing with the
  sandbox just want to see how Oscar works and want to get it up and
  running as quickly and easily as possible.

* Oscar extensions also suffer from the same problem.  Eg, you would
  have to get lessc installed even if you had no interest in playing
  with Oscar's styles.

I think it's better to have the CSS files committed and simply to be
careful about pull requests and commits that change the CSS.  Before
releasing, we need to ensure that the CSS files correctly generate from
the LESS files.

This commit also changes the default sandbox set-up to serve the CSS
files but compressed.

Relevant to #605, #546, #246
Merge pull request #607
set Zip/PostCode not to be required

Some countries, ie. Ireland, don't have post codes, so:
1) post code should not be a required field
2) maybe conditional validation making PostCode required for some countries