Add empty static directory

This saves having to create it when trying to get the sandbox up and
running. Empty directory is committed via a tricky .gitignore file.
Update tox.ini to test against released Oscar 0.7
Support new Django Debug Toolbar
Housekeeping

* Add comment for breakage with django_extensions and modern PostGIS
* Use same settings_local file for tests and sandbox. Test runner
  appends test_ anyway, so a different database gets used.
* Add missing flatpages app
* Move out i18n URLs as required by Oscar 0.7
Bump version to 0.6.1