Removed self.objective

self.objective in ant was unecessary. Removed and broke tests.
Broke

Removed self.objective from ant.move and seem to have got simulation
stuck in a loop.
Fixed previous broke

self.__moves__ of ant was getting full and filling memory I assume.
Written so it actually clears each ant.move()
More broken tests

Broke simulation test as it needs something better for checking for
pheremones.

ant test for move near hive needs improving.
Removed some guff and implented decay rate

Removed some guff from tests. Added some more TODOs. Implemented a decay
rate and wrote associated tests.