Enhance the inclusions commands

[sethfowler]

The following features would make the inclusions commands more useful:

• Add the ability to filter out standard library inclusions. This is particularly important for inclusion-hierarchy.
• In inclusion-hierarchy, note which identifiers are referenced from each inclusion. This will make it easy to sanity-check your inclusions.

[sethfowler]

There also needs to "single-step" versions of these commands that just show immediate inclusions/includers.

[sethfowler]

That's the hard part. The rest of this can probably be handled by a combination of:

• Rendering the dot graphs on the client side. (Probably the best bet for filtering out the standard library inclusions - can just remove every node which has a label that doesn't start with the project root path.)
• A 'bound' parameter to limit how deep of a graph gets generated in the first place. It's unimportant if this happens client-side or server-side for this command, but it will matter much more for the call hierarchy graph, so I'm inclined to see what happens there before implementing this.