Be able to Delete/Clear Initiative Dates

Once the Initiative Start and Duration End dates are populated, they cannot be cleared. We should be able to clear the Duration Start and Duration End dates for an initiative once it has been set.

A use case for wanting to remove the dates from initiatives would be that we want to have them in the system, but there is no current backlog with which to hold them (there's an idea!).

We don't plan on moving forward with the initiatives, or even starting them for some time, so we'd prefer them not to have dates than to have dates set into the future (our workaround).