Add tests for RouteComposer (refactoring on the way)
Refactor Graph DI; rewrite much of GraphTest with mocks
Rename RouteComposer to LeafNodeRouteFactory
Add DjikstraResult to give access to both leaf nodes and entire graph
Refactor route augmentation:
 - DjikstraResult now responsible for creating routes
 - RequiredTraversalAppender creates new routes when an untraversed method doesn't start at a leaf node
Pull a DjikstraResult creation into a factory, to hide 'new's