Refactor GraphService. Add GraphSource.
Add GraphServiceImpl unit testing.
Use File to extend paths.
Extract path to input stream code from loading.
Load graph from classpath.

Note: This code is a bit useless for now as the primary
goal of loading graph from classpath was to embed graphs
in webapp WAR files. As long as we do not support webapp
containers this class is probably useless.
Add @Override to overriden method.
Add unit-test for file-related graph service methods.
Do not register graph when problem loading.
Add throws clause to getGraph(...) methods.
Allow call to reloadGraph in memory graph source.
Evict graph if reload fails.

Forbig registering null graph.
Update GraphService unit-test.
Evict graph when null in getGraph().

This will be useful for auto-reload that badly failed.
Re-implement graph autoreload within new framework.
Keep old graph in case of graph load failure.
Comment parameters, disable autoscan if 0.
Only create ScheduledExecutorService when needed.
Remove deprecated auto-discover graph service.

The auto-reload feature is implemented as option in FileGraphSource.
The auto-scan feature will be implemented as option in GraphScanner.
Better log, explain more.
Add auto-reload option to GraphServiceImpl.