Using contestData could be optional (by election or contest?)

[JohnLCaron]

Could make contestData optional (by election or contest?). Likely not always needed.

data class Contest(
override val contestId: String, // matches ContestDescription.contestIdd
override val sequenceOrder: Int, // matches ContestDescription.sequenceOrder
val contestHash: UInt256, // eq 58
override val selections: List,
val proof: ChaumPedersenRangeProofKnownNonce,
override val contestData: HashedElGamalCiphertext, // TODO make optional?
val preEncryption: PreEncryption? = null, // pre-encrypted ballots only
) : EncryptedBallotIF.Contest {

Savings is
EC: 33 + messageSize + 32 + 4 = typically 133 bytes
IG: 512 + messageSize + 32 + 4 = typically 612 bytes
messageSize = (1 + contestLimit) * 32