Rename project fields date fields so they aren't confusing

Currently, projects have 2 fields besides start date:

• Close date: The date the tournament wraps up and prizes will be paid. All questions that should be included in the leaderboard must close and resolve before this date. This is displayed on the front end as the “Winners announced date”
• Forecasting end date: The date the last scored question that counts for the tournament closes. The date shown is the latest of the Forecasting end date and the latest question close date closing and resolving before the Close date.

The Forecasting end date is labelled "Closes" on the front end.

We should rename Close date to “Winners announced date” and Forecasting end date to "Close date".