Remove ranked ballots containing specified candidates

[peterrrock2]

Summary

Add a profile cleaning function that removes every ballot containing one of a specified set of candidates or CVR markers.

This supports workflows where ballots containing values such as "overvote" or an invalid write-in marker should be excluded entirely rather than having the marker removed and the ballot condensed.

Expected behavior

Given ballots:

RankBallot(ranking=["A", "B"])
RankBallot(ranking=["A", "overvote", "C"])
RankBallot(ranking=["C", "A"])

filtering on "overvote" should retain the first and third ballots and remove the second.

Part of #337.