Initial commits for effort to genericize mutators based on graph operations
Added edge endpoint add/delete

Added operation to batch delete elements based on range
Refactored add/delete operations into final classes
Updated documentation
Refactor getEdges to use Vertex object
Collect element caches into single object
Move getVertices() into VertexTableWrapper
Move getProperty and getPropertyKeys inside AccumuloElement

Other cruft cleanup
Property updates

Moved removeProperty to AccumuloElement
Added property cache unit tests
Moved flushing to GlobalInstances
Cruft cleanup

NOTE: Unit tests failing due to what appears to be race condition