Extract module counter into its own class.
update ModuleReferenceCounter
adjusted modules to use new class ModuleReferenceCounter
made the refCounter declaration lazy and consistent with data source example
renamed ModuleReferenceCounter to IngestModuleReferenceCounter as requested, the class now removes entries once they decrement to zero, and removed static creation methods from sample classes
added a shutdown() to do counter decrements
Merge pull request #615 from SynapticNulship/module_ref_counts

Module ref counts
Merge branch 'develop' of https://github.com/sleuthkit/autopsy into keywordSearch