Ability to end a poll

Two suggestions/observations from using your polling function:

1. Allow creator to enter an end date so people are not allowed to "vote" after a certain time period.

2. The CSV export has a bug OR needs information added to it. If a reader makes a selection on the poll then returns a day or more later and makes a selection again on the same poll, the app view shows the last date they "voted" but the exported CSV only shows the first date they "voted." I think both of those pieces of information should be in the report.