Don't error on importing modules that require a Kenya database

It's now possible to have COUNTRY_APP set to Kenya without
the Kenya database being present, so make sure that just importing
these files doesn't throw an exception because the PlaceKind
or PositionTitle objects can't be found.

These scripts were only of use for importing data from the Kenyan
election API, so fixing this more elegantly isn't a priority.
Add fallback templates for when no country is set

This is primarily to stop test failures when running generic
tests with COUNTRY_APP set to None, but also is a step towards
having a generic Pombola theme which can then be customized
for particular countries.
Add settings modules for countries and country-specific tests

With these changes, you can now run the tests for a specific
country with, e.g.:

   ./manage.py test --settings=pombola.settings.tests_south_africa
   ./manage.py test --settings=pombola.settings.tests_kenya

... regardless of what COUNTRY_APP is set to in your general.yml

(The non-country-specific tests can still be run with:

   ./manage.py test --settings=pombola.settings.tests )

It also adds settings modules specific to particular countries,
and manage.py has been changed so that when you run, e.g.:

   ./manage.py runserver

... and COUNTRY_APP in general.yml is set to 'nigeria', the
settings module used would be pombola.settings.nigeria.
wsgi.py has similarly been changed to use the settings module
specified by COUNTRY_APP.

This commit incidentally also makes it possible to run pombola
with COUNTRY_APP set to None, a benefit of this being that it's
a useful step to having a generic theme, as with Alaveteli, that
can be overridden and elborated by other implementers.

A further advantage of this change, beyond being able to run
country-specific tests regardless of your COUNTRY_APP settings
in general.yml, is that various country-specific setttings no
longer have to be specified in general.yml, such as:

  OPTIONAL_APPS
  BLOG_RSS_FEED
  BREADCRUMB_URL_NAME_MAPPINGS
  TWITTER_USERNAME
  TWITTER_WIDGET_ID
  MAP_BOUNDING_BOX_NORTH = -22.06
  MAP_BOUNDING_BOX_EAST = 32.95
  MAP_BOUNDING_BOX_SOUTH = -35.00
  MAP_BOUNDING_BOX_WEST = 16.30

... since they're determined by the country, and now kept in
pombola.settings.[COUNTRY_APP]_base.
Remove old test-running scripts, replace with a new one