Reservation as option with time period

[developeregrem]

If the status "Option" is selected when creating/editing a reservation, another input field for entering the date (option to) should appear (default is 1 week from current date).

In the popover of a reservation (mouse over reservation) the end date should appear with an option.
If the option has expired, this should be indicated by a small icon (perhaps next to the name) (in the reservation overview).