Converting HaploBlocker to use NodeTraversals

[josiahseaman]

Currently, we have a working Database that supports ZoomLevels and we have a HaploBlocker algorithm that could produce ZoomLevels. However, the HaploBlocker implementation doesn't use the same objects and it hasn't been tested on non-linear graphs yet.

• Object references changed
• Object construction updated to NodeTraversal.objects.create()
• Iterating over "all nodes" handled in a reasonable consistent order
• Testing for non-linear test cases where summarization could trip over itself.