Add Whelk reasoner.

[balhoff]

Add Whelk as a reasoner choice.

• docs/ have been added/updated
• tests have been added/updated
• mvn verify says all tests pass
• mvn site says all JavaDocs correct
• CHANGELOG.md has been updated

[jamesaoverton]

My only concern is increasing the size of the binary by ~15%:

branch	link	size
master	https://build.obolibrary.io/job/ontodev/job/robot/job/master/	62.36 MB
whelk	https://build.obolibrary.io/job/ontodev/job/robot/job/whelk/	72.39 MB

What are the key benefits of Whelk for ROBOT?

[balhoff]

My only concern is increasing the size of the binary by ~15%

This was surprising to me, since Whelk is tiny and I have tried to keep the dependencies minimal. The core has only one dependency (scalaz-core) which is used for a couple small things; it turns out it's a lot bigger than I realized! scalaz-core accounts for pretty much all of that. I'll just re-implement the one method I'm using—hold off until I update this PR.

What are the key benefits of Whelk for ROBOT?

Whelk provides a combination of OWL features not available together in any of the other reasoners:

• EL scalability (albeit slower than ELK)
• better support for Self restrictions than ELK, supporting rolification
• some classification for unions
• object property assertion materialization
• OWL RL features for Abox
• SWRL rules (class and object property atoms)

Whelk is also much faster than ELK at answering DL queries, but I don't think this will be apparent in the current ROBOT commands.

[jamesaoverton]

Thanks. Now I see 63.00 MB.

The changes look good. I want to try it out on a couple of things before merging.