We currently mention it in internals/sandbox.rst. I've added a note to
the dashboard app (ref/apps/dashboard.rst), the sandbox/urls.py and
expanded on the feature explanation on index.rst.

Fixes #816

They were missing the autodoc documentation for views (abstract) and
abstract models.
Also added two docstrings to the views in the promotions app to have
them showing in the autodoc.

Also adds a docstring to the is_discountable AbstractProduct

* Use correct directives in signals.rst
* Removed newline in glossary.rst that broke sorting of glossary terms
* Removed syntax warning for upgrading.rst

Some of them are rather basic, but it's a start.

Fixes #697

* Better wordings for the individual steps
* Mentioned necessary copying of migrations directory
* Fixed wrong prerequisites in examples
* Glossary typo fixed

Commonly used terms should be explained there.

- Added stubs for both apps
- Switched to using :automodule: for abstract models instead of
  individual :autoclass:
- Added instructions on creating a Partner and ProductClass instance
  when setting up a new Oscar instance

Plus some general reorganisation.

Fixes #608

OSCAR_REQUIRED_ADDRESS_FIELDS allows setting which fields are required.
The use case is that post codes are expected to be required, but many
countries don't actually use them.

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

Also grouped promotion settings together.

To set a base for upcoming docs changes, the docs directory structure
has been streamlined to follow a simplified version of Django's docs.

The old _draft folder has been removed. Both files from there and the
current docs that don't fit nicely into the new structure are in _old/
for the moment.