Switch to using the master branch of MapIt
Add a command that imports the 2013 election boundaries

This uses the generic mapit_import script via
django.core.management.call_command.
Title-case the names of the 'dis' areas

This is for consistency with the previous generation, which
has all-caps constituency names but title-case county names.
Correct some county names that are wrong in the source data

Fixes #511
Create a ParliamentarySession model and associated migrations

This is intended so that Place and Position objects can
have a foreign key to the particular parliamentary session
that they're valid for.  It also associates that session
with a particular generation in MapIt.  (I'm not sure
about this particular choice, and there's a comment in
the code to that effect.  Currently it's unused.)

This commit also changes the Place model to add a foreign
key to ParliamentarySession and add the migration.
Display the ParliamentarySession for Places in lists of them
Add a method to return ParliamentarySession objects for a PlaceKind

Each Place can have a ParliamentarySession specified for it.
This commit adds methods to PlaceKind that return all
ParliamentarySession objects that are specified for a Place
of that PlaceKind.

There are two versions, one which returns [None] if no
ParliamentarySession objects were found (e.g. as for
places of the "Country" PlaceKind) to make it more easy
to iterate over the sessions in a template.
Add methods dealing with dates to the ParliamentarySession method

This adds:

  - a covers_date method, for testing if a date is during a
    the session

  - a default ordering by the start date of the session

  - add a relative_time method, to return "Past", "Current"
    or "Future" for the session
Change the place_kind view to deal with parliamentary sessions

Now, instead of having multiple PlaceKinds to represent
constituencies at different points in time, we just have
one PlaceKind for 'Constituency', and Places of that
PlaceKind have a particular ParliamentarySession.

This commit changes the place_kind view to iterate over
sessions for a particular PlaceKind rather than just
each PlaceKind.
Add a command to create parliamentary sessions and migrate places

This command is intended to be called from a datamigration to
make sure that ParliamentarySession objects are created for the
known sessions in Kenya and Nigeria, and make sure that the
PlaceKind and Place objects are updated correctly.

Note this uses settings.COUNTRY_APP to distinguish which country
this instance of Mzalendo is for, so it also adds a note to that
effect to general.yml-example.
Add a datamigration for Nigeria and Kenya's parliamentary sessions
Merge branch 'boundaries-2013'