updateProjectActivityType nillable fields

In the FY20 schema, projected and actual values for start date, completion date, and total cost were all nillable in the updateProjectActivityType, allowing for a value to be cleared out, if appropriate. However, this is missing from the FY21 schema, and, since blank values appear to be disallowed, there is no way to clear these values. Hopefully this was just a typo as changes were made related to allowing activity name (and hopefully description) to be updated.

There are two reasons for these options to be available. First, there are some cases where a project may provide data for a parent activity either unintentionally or before deciding to make a child activity a parent. In either case, while the dashboard may ignore the data in favor of rolling up the data, at least in the past, the data still existed, so clearing it was important to ensure there was no confusion.

Second, while uncommon, it was possible that some activities might want to remove the projected data when the actual was provided. As changing projected data has never required a revise operation, this still should be allowed. (Of course, changing the actuals does require a revise, but the first example is why those fields are still nillable - and the submission logic still generates an error when attempting to update an actual field without a revise.)