Make access check function for dashboard easier to customise
* It can now be specified in OSCAR_DASHBOARD_DEFAULT_ACCESS_FUNCTION
* nav.py and menu.py were split up so that Node can be dynamically
loaded and hence overridden
I recently needed to alter the access function and realised it's not as
easy as I thought.
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.
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.
Clean up documentation typos (e.g., use 'e.g.' instead of 'eg'; misspellings; GitHub vs Github; consistent use of Oscar vs oscar or django-oscar when referring to the product)