Increase mass when growing.

We have to sort out how to handle "biomass" and "mass" though.
We're also marking the altered properties as unseen, so that they are
sent in updates.
Fixed incorrect handling of delegates.

We should only stop if the op is blocked.
Properly remove properties with delegates.
Move terrain eat handling to property.

This follows earlier work where we've moved more and more functionality
out of the entity classes and into properties. One of the goals of this
change is to allow for the "terrain" property to be added to arbitrary
entities.
Updated tests.

Started initial work on providing stubs, so that we finally can start to
reduce the amount of code needed for the tests. Some tests are using the
new stubs, but the plan is to continously move more and more code from
the tests over to the stub as they are updated.