Deleting candidates who had nominations can break offices page

[kochman]

Candidates who had entered nominations and were then deleted still have nominations in the database. This causes the offices page to fail to load nomination counts for candidates if there are no longer any candidates running for that office, since the controller tries to iterate over a property on the office that has not yet been defined (candidates).

Two things should be done:

1. Deleting candidates should remove their nominations
2. Candidates should always be defined as an empty list