Decide how to deal with STV CVRs

[vteague]

Although we are not required to audit STV contests (i.e. multi-winner preferential contests), we need to ensure that colorado-rla does not break when they are uploaded. This requires a bit of thought. Probably we want three types of contests: plurality, IRV and STV.
Probably:

• when parsing, a contest with ranks and multiple winners should be STV,
• STV contests should be always NOT_AUDITABLE
• STV contests cannot be targeted for audit
• STV winners should have a clear placeholder (e.g. UNKNOWN or "") - note that the default contest counter will get the wrong winner, just as it does for IRV.
• STV estimatedSampleSizes and optimisticSampleSizes should match the values for other NOT_AUDITABLE contests. (I have a vague recollection that this is 0, but we should check.)

Think about whether we could easily get a count of 'other discrepancy' in the event that an STV contest happens to be on an audited ballot.

Consider whether all this is best achieved with an STVComparisonAudit class.

[vteague]

This will probably also need to update ReportRows::genSumResultsReport, just to make sure the tallies computed by countContest are not output for STV (where they will be wrong).