Breaking changes to UnitDelivery SW

The missions weren't set correctly. This should be changed to Area Guard, and Harvesters should be sent to harvest.

Remove support for Deliver.Buildups=, because it actually never worked correctly for AI, and salvaging it failed. Instead, assume it is enabled (this is the case that worked).

Allow placing units on cells containing Tiberium. There's no reason not to do this, but it's not really worth a new tag. Thus, this is a breaking change.