Test for data-loading-text directly

This reduces API complexity at the cost of removing the possibility to get
the pure bootstrap behaviour that doesn't check for invalid fields. I
cannot imagine a use case where the pure bootstrap behaviour is better, so
I took the opportunity to reduce complexity.
Update and minimize jquery-ui

So that it doesn't unnecessarily conflict with bootstrap's $.fn.button().

This is a jQuery UI custom download with just the components we currently
use:

* Version: 1.11.2
* Interactions
  * Sortable
* Theme: Cupertino

(Other dependencies get selected automatically.)
Remove jquery copy in jquery-ui

We get our jQuery elsewhere.
Allow easy overriding of jquery-ui

In case an oscar implementation needs more components than standard oscar
Copy disable-on-submit functionality over from frontend to dashboard
disable-on-submit all submit buttons: frontend
disable-on-submit all submit buttons: dashboard
disable-on-submit all submit buttons: sandbox
disable-on-submit all submit buttons: demo site
Improve docs for Application.permissions_map

This just led to confusion, so I decided to improve the docs a bit.

We really should be using Pytohn sets instead of lists for this.
Merge pull request #1554 from machtfit/disable-button-on-submit

Disable button on submit
Recompile CSS files

See https://github.com/django-oscar/django-oscar/commit/8e2b12647ba78a749b73c804d5d7c9df52d81afa#commitcomment-8502671
Remove conditions and benefits

Remove the conditions Coverage, Value and Count and the benefits
AbsoluteDiscount, FixedPrice and Multibuy. Add NoneCondition for offers that
apply to all baskets.

Reason is that the correct semantics are unclear and we don't need them now
and I don't want to spend time fixing the tests for them. I'll refactor
offers without them.

Example for unclear semantics:
https://groups.google.com/forum/#!topic/django-oscar/vceEpy889O4
https://groups.google.com/forum/#!topic/django-oscar/XMuhEBLbv-U
Refactor offers

To track benefit application on a separate data structure instead of the
basket line. This uncouples the database-bound basket from the offer
calculations.
Support multiple benefits per line