Seperation of world and memory graph

[trav-d13]

Separate MemoryGraph from the World implementation such that a memory graph is operated on by the world (i.e. it holds a reference to rather than extends) and create ACOworld and WFworld classes that extend and modify the behaviour of World.

Endstate:
1 - World holds a reference to MemoryGraph
2 - ACOworld extends World with addNew and neighbour modified
3 - WFworld extends World with addNew and neighbour modified