Update fixtures to reflect removal of is_canonical

is_canonical has been removed recently; this commit updates the JSON
fixtures to make the sandbox accordingly.
Fix example code in Getting Started docs
Mark more strings translatable

Fixes #1171
Correct handling of offer creation without a range

The workaround for JSON serialisation introduced a bug that was
triggered when the offer contained no range, which is allowed for
certain offer types. In that case range is None, and accessing range.id
threw an error.

Fixes #1167. Thanks to @izidormatusov for reporting.
Remove hard-coded user model in recent migrations

This ensures a custom User model can be used with migrations.
Attach basket to request before applying offers

apply_offers_to_basket may depend on it, so we attach it before calling
that.

Reported and code supplied by @vovanbo. I re-did the work to add
comments.

Fixes #1172
Merge branch 'master' of https://github.com/tangentlabs/django-oscar into feature/demo-multipayment-with-faceted-catalogue
Add dependency for recent migrations
Merge branch 'master' of https://github.com/tangentlabs/django-oscar into feature/demo-multipayment-with-faceted-catalogue
Spellchecking
Introduced 'mincount' field for settings.OSCAR_SEARCH_FACETS instead of 'show_zero' to match solr's config values. This parameter allows to include zero-counted facets in search result.  Default value is 0. Also 'limit' field added to fix default Solr behavior which limits max facets count to 100. Negative value means no limits.