Support explicit closing a poll and avoid the misleading term expired

[dartcafe]

The term expired poll could mislead users, if a poll was closed by the owner via setting the current moment as expiry date. In this case no announced expiry time was announce before. This can cause confusion.

• Add a button to explicitly close the poll
• Change the term expiry to closing date
• Change the term expired to closed
• replace items
• Change intial closing date to 1 week in advance
• Change route names
• Change properties and methods