Faster is better!

Only search_default needed correcting.

- Add new block for payment tab
- Rename transactions block
- Provide transactions in get_context_data
- Better handling of empty iterables

is_highlighted is now an integer and works similar to the common
"ordering" fields. The higher the number, the higher the country will be
moved up in the list.

Fixes #720, #725

Filenames can easily get longer than 100 characters, and that causes
Django to fail hard (I think with a DatabaseError), because it's
currently not validated (see Django #11027)

This fix increases the character limit to 255 chars. Going much higer
can cause trouble with MySQL.

Fixes #625. Thanks for reporting go to @soloweb.

To be consistent with the rest of Oscar.

This makes more sense than keeping it as a method.

Hattip to @BuddhaOhneHals for doing this in the first place.
Unfortunately, I couldn't (be bothered to) merge the original commit as
the merge conflicts were too painful to resolve - simpler to just
reapply the same change myself.

Fixes #466

Update release notes too.

The parameters have been changed to use request, not request.basket.