Batch updates in dropIndex to smaller transactions. 
Added a few accessers to the class.
Changed createIndex function to add empty in-out list for forbidden
nodes.
Updated unit test.
Merge branch 'experimental' of https://github.com/SciCrunch/SciGraph.git
into experimental

Conflicts:
	src/main/java/edu/sdsc/scigraph/internal/reachability/ReachabilityIndex.java