Use owltools to strip some axioms from Uberon module. Fixes #5

Some logical axioms in our extracted uberon-module.owl were causing
HermiT reasoning to fail. I added instructions for using owltools
to reduce the number of axioms in Uberon. This makes the extracted
module smaller and fixes the reasoning problem.

- updated Using and Reusing section with owltools instructions
- updated uberon-terms.txt to force extraction of some high-level terms
- updated uberon-module.owl example, now much smaller
- updated application.owl to remove unused subClassOf axioms
- updated obo-tutorial.owl, merging newest results