applies_to_tax_exclusive_prices has been removed in f03a7e8

Cherry-picked from #1414.
Fix typo in offers docstring

Cherry-picked from #1414.
Allow access to all non-voucher offers in offers dashboard

Cherry-picked from #1414.
Don't create objects in the database unless necessary

Conflicts:
	oscar/apps/offer/models.py
	tests/integration/offer/combination_tests.py
	tests/integration/offer/percentage_benefit_tests.py

@maikhoepfel duplicated the proxy class short-circuit logic for
Conditions as part of this commit.

Cherry-picked from #1414.
Apply offers in order of descending priority

This already worked only within site offers by way of default model
ordering. Site offers are probably the most common offers, however the
ordering of all offers has to be controlled by the applicator.

Conflicts:
	tests/integration/offer/applicator_tests.py

Cherry-picked from #1414.
Fix docs build errors

Had to rename to new method name and re-add a link.
Update i18n files

Pulled from Transifex.
Update LANGUAGES in settings with new languages

We have new translations above 50%, so they're added to the sandbox.
Update AUTHORS file with new contributors

No secret sauce there:
https://github.com/tangentlabs/django-oscar/wiki/Releasing#contributors