Mostly winner -> payment (vote)

[UdjinM6]

Followup for the recent winner_block PR (#1028) and name confusion discovered during code review.

"Mostly" because also:

• CMasternodeBlockPayees::GetPayee - > CMasternodeBlockPayees::GetBestPayee which describes what this function is actually doing a bit better imo;
• fixing constructor CMasternodePaymentVote empty constructor https://github.com/dashpay/dash/compare/v0.12.1.x...UdjinM6:renameWinnerToVote?expand=1#diff-58a24cc2e98df19ec79c042c0729cd89R113.