Also include candidates without data in /api/candidates

This is relevant to #133 because we're going to add all candidates to
the table, regardless of whether they have funding. But if they don't
have funding, we can't get them from the database! So, this adds a bit
more logic to the /api/candidates endpoint to look at the
Party::CANDIDATE_INFO constant to see which keys are not in the
Party::MAYORAL_CANDIDATE_IDS array and instantiate new Party::Committee
objects with that data.
Use candidate name in URL

So the url is #candidate/libby-schaaf instead of #candidate/1234.
This is necessary for candidates that aren't persisted in the database.
Skip summary section for candidates with no data
Merge pull request #146 from tdooner/candidates_with_no_data

Candidates with no data