Remove unused CSS

There's no category-selected in the Dashboard as far as I can find
Actually use the variables from variables.less
Set a bigger font size and more readable font

The previously used font was too thin.
Add bootstrap style for select2

From https://github.com/t0m/select2-bootstrap-css
Visually connect tabs with tab content through a well
Don't mess with my CSS like this!
Use more down-to-earth z-index.

The effect is the same.
Remove deviations from stock bootstrap that caused problems

They came into oscar mostly in several-1000-lines commits with messages
like "dashboard improvements", so there's no way to find out why they were
added.
Reduce whitespace above black bar at the bottom and the form above
Undo border color changes that didn't catch all borders
Add CSS to vertically align plain text with the label in a horizontal form
Undo this bootstrap modification. It makes things harder to read.
Merge branch 'get-model-problem-workaround' into machtfit

* branch get-model-problem-workaround:
  This is the real fix. Hopefully.
  Just log that for now until we figure this out.

https://github.com/tangentlabs/django-oscar/issues/1205
Merge branch 'django-tables2' into machtfit

* branch django-tables2:
  Move queryset_{description,icon} to Table class
  Move users list to django-tables2
  Remove pointless num_orders template tag
  TODO
  Allow table icon customization
  Move dashboard categories list to django-tables2
  Move table caption into <table><caption>
  Keep current tab and ordering when returning to the list after editing
  Move the dashboard product list to django-tables2

https://github.com/tangentlabs/django-oscar/pull/1173
Merge branch 'offer-improvements' into machtfit

* branch offer-improvements:
  The code handles the no applicable lines case well without this statement
  Make Benefit classes more reusable
  Don't break sentence spelling/grammar in German.
  Allow specifying other model attributes when creating custom benefits or conditions

https://github.com/tangentlabs/django-oscar/pull/1392
Merge branch 'refactor-offers' into machtfit

* branch refactor-offers:
  Fix typo
  Allow access to all non-voucher offers in offers dashboard
  Apply offers in order of descending priority
  Support multiple benefits per line
  Refactor offers
  Don't create objects in the database unless necessary
  Remove conditions and benefits
  applies_to_tax_exclusive_prices has been removed in f03a7e8
  The code handles the no applicable lines case well without this statement
  Make Benefit classes more reusable
  Don't break sentence spelling/grammar in German.
  Allow specifying other model attributes when creating custom benefits or conditions

https://github.com/tangentlabs/django-oscar/pull/1414

Conflicts:
	oscar/apps/offer/models.py
Merge branch 'title-fix' into machtfit

* branch title-fix:
  This was forgotten in d3ddfa5

https://github.com/tangentlabs/django-oscar/pull/1421
Merge branch 'checkout-refactor' into machtfit

* branch checkout-refactor:
  WIP Refactor checkout
  Remove commented code

https://github.com/tangentlabs/django-oscar/pull/1423
Merge branch 'fix-fork-apps' into machtfit

* branch fix-fork-apps:
  Add missing newlines
  Fix deprecation warning
  Fix oversight

https://github.com/tangentlabs/django-oscar/pull/1428
Merge branch 'rework-order-comm' into machtfit

* branch rework-order-comm:
  Rework order emails.
  Don't create CommunicationEvent here

https://github.com/tangentlabs/django-oscar/pull/1437