Update phonenumber dependency

This is to avoid https://github.com/nvie/pip-tools/issues/50 so that
pip-compile (from pip-tools' future branch) can be used to pin
dependencies. See also http://nvie.com/posts/better-package-management/.
Bump Django versions

A bugfix release for 1.7 was released which contains many migration
fixes. Also bumped the minimum 1.6 version as we were already lagging
two releases behind.
Transifex: Don't push translation

A Travis CI bot automatically extracts the source strings and pushes
them to Transifex. Previously, this bot also pushed translations, which
does not make sense, as the translations are made at Transifex.
Surprisingly, this didn't seem to cause much trouble - my best guess is
that Transifex respects modification times and ignored the pushed
translations. It certainly does so for source files.
But @mvantellingen reported that Dutch source files were overwritten. I
just did a manual push of only source files, and the Transifex UI still
shows all languages as updated. It makes sense as the source strings
changed, but makes me wonder if Michael saw actual overwrites.

Either way, pushing translations was the wrong thing to do. And as
nothing should go wrong with the English source file, I removed the skip
flag.

I intent to re-enable the bot once we've released 0.8.
Fix cursor:pointer for labels on dashboard statistics

The totals displayed on the store statistics are <label> elements, which
causes a mouse cursor suggesting they're clickable. This commit fixes
that.

@maikhoepfel rebuilt the CSS with less 1.7.5. Annoyingly, even without
this change, all the sourcemap files were updated by that. No idea why.

Closes #1526.
Merge pull request #1524 from machtfit/update-phonenumber

Update phonenumber dependency
Import models module instead of relying on import_models()

After feedback from @aaugustin, the fix for the Django 1.7 model loading
regression (done in 51a0859) can still interfere with the process. The
clean approach is to emulate importing the models file.

The code was provided from @aaugustin; I merely tested it still fixes
the issue and fiddled with the comments to appease the gods of PEP8.
Add get_facet_munger method to SearchHandler

Without this you can't modify `FacetMunger`'s constructor.
Conflicts:
	oscar/apps/search/search_handlers.py

Closes #1536.

@maikhoepfel added PEP8 fixes for the search app.
WIP Refactor checkout

This decouples the checkout flow from the individual checkout views.

There are now three checkout view mixins:

  1. checkout.session.CheckoutSessionMixin puts relevant checkout info in
     the template context. Pre and skip condition code has been removed.
  2. checkout.mixins.OrderPlacementMixin as before has the meat of making
     an order from a basket and handling payment. After placing the order
     control is returned to CheckoutFlow.
  3. checkout.flow.CheckoutFlow is new and manages the checkout flow.

CheckoutFlow provides checkout(), which uses the checkout session data to
determine the next step in the checkout, and redirects there. If all
steps are complete, it lets OrderPlacementMixin handle the basket to make
an order.

If a redirect payment method is used, the payment result view can call
checkout_failed() or checkout_successful() to return flow control to
CheckoutFlow. checkout_failed() will show the preview page again, and
checkout_successful() will redirect to the thank-you page. This allows
customizing this part of the flow independently of the payment
implementation.

The individual checkout views were stripped of pre and skip conditions and
other checkout flow code. The all use the CheckoutFlow mixin instead of the
CheckoutSessionMixin or the OrderPlacementMixin.