Canonicalization - automatically associate nominations with a work

[offbyone]

Using some kind of lookup, assign nominations to a work.

The algorithm, roughly, will be to assign them to a work if any other nomination having the same work string is associated with it, across all categories in the election. That should take place when the nomination is saved to the database.

This will need to be tested in the nomination view tests, especially with ballots updating

[offbyone]

This was implemented in #217, specifically in 172c35e and bd5d78f