Update the submodule to get updated PPC data
Consider PPC scaper data most authoritative; overwrite different values

Ideally we would check if there had been an intervening non-automatic
edit and only overwrite if not, but that's a bit more complex to implement,
so for the moment this new behaviour (always overwrite) is preferable to
just warning and not overwriting, I think.
Rearrange the order of constituency name tidying
Remove some unnecessary indentation
Import PPCs: add an option to just check constituency names
Add some constituency name corrections
Add a couple more PPC matches
Insist that person IDs only consist of digits and update tests

The test data still used slugs as IDs, so this commit changes that, and
makes sure that the IDs in the test data match those in the current
YourNextMP database, just to avoid confusion.

A couple of tests needed their mocks updated as well; previously they
would pass a person ID which was an automatically generated mock return
value, but now that it's required to be only digits, the reverse creates
an error. This means setting mock_popit's return value for persons to
FakePersonCollection in a couple of extra places.
Fix the 'DateTimeField received a naive datetime' warnings
Remove debugging output that's no longer particularly useful

... and which clutters up the test output.