Ignore third parties and permitted participants, keep political parties
Suggest an alternative CSV URL with de-registered parties too
Also send the 'register' ('Great Britain' / 'Northern Ireland') to PopIt

This might be useful at some point, so let's make sure it's in the PopIt
database too.
Also include the dissolution_date for de-registered parties
Include the complete EC identifier in 'identifiers'

We use a version of the EC identifier as part of the ID field of the
organization, but it might be useful to have the complete identifier
(with the PP or PPm prefix) in the PopIt database as well.
Import the election dates from models.py instead of redefining
Also add a slug for each political party
Remove an unused variable
Match up Electoral Commission parties with YNMP parties where possible

This is done by matching names after some simple mangling into a key
(downcasing, removing non-alphanumeric characters, etc.)

For the few parties that couldn't be matched like this, we create them
but with a different ID scheme, which looks like ynmp-party:1234]
indicating that the party ID in the YourNextMP dump was 1234.  If the
party could be identified against an Electoral Commission registered
party, the ID will be something like party:5678, where 5678 is the
numeric part of the Electoral Commission party for that party.

This means that two pseudo-parties are created:

  'Independent' (ynmp-party:2)
  'Speaker seeking re-election' (ynmp-party:12522)

The other unmatched cases are these single constituency errors:

  British Unicorn Party
  Radical Reform Group
  New Independent Conservative Chelsea and Fulham
  Neath Port Talbot Independent Party
  Scottish Senior Citizens Unity Party
  National Liberal Party, The Third Way
Fix some indentation
Make the message about maximum person ID a bit more specific
Remove extraneous trailing empty lines
Add a helper shell script to create the PopIt instance from scratch