Whitespace.
Fix test loading when called with `ruby`.
Strip blank HistoricalAccount political party IDs.
Reject garbage HistoricalAccount political parties.

Invalidating rather than skipping in this case to
provide proper feedback for mistakes.
Merge pull request #833 from alphagov/55910960-historical-accounts-bugfix

Historical accounts bugfix

https://www.pivotaltracker.com/story/show/55910960