Update redis to 3.3.2

Update ipdb to 0.12.1

Remove collections ABC deprecation warning

`DeprecationWarning: Using or importing the ABCs from 'collections' instead of from 'collections.abc' is deprecated, and in 3.8 it will stop working`

Simplify AppConfig when forking

We aren't changing `label` or `verbose_name` so let's use class inheritance instead

ref https://github.com/django-oscar/django-oscar/issues/3080

Remove detox from docs

Use built-in venv module to create virtualenv

detox is unmaintained and tox has a parallel mode

Use `get_model` to import `ConditionalOffer` in basket's `utils`

Update ipython to 7.6.1

Update pillow to 6.1.0

Update django-debug-toolbar to 2.0

Update isort to 4.3.21

Update psycopg2 to 2.8.3

Update checkout payment detail template: cleanup archived packages, replace with the relevant ones.

Restore voucher set URLs

As part of fbf8bac4c5/, the Voucher set URLs disappeared.

The following exception is logged on every Dashboard page:
`Reverse for 'voucher-set-list' not found. 'voucher-set-list' is not a valid view function or pattern name.`

Doc Fix: Link to stable documents in front README page

Update django-extensions to 2.1.9

Upgrade CDN version of jQuery

https://github.com/django-oscar/django-oscar/pull/3018 updated the in-tree versions

Add sorl-thumbnail to docs requirements

Update isort to 4.3.20

Update django-extensions to 2.1.7

Update werkzeug to 0.15.4

Update requests to 2.22.0

Add less.js to Dashboard Layout

* Retrieving product options now performs only 1 query.

Also it returns all the product options combined. This makes more sense because
as the existing tests prove, there is already a way to retrieve the product_class
options and the product options separately.