Integrate tests into the SbolTestSuite continuous integration process.

[palchicz]

This involves making sure that the github repository runs the tests against LibSBOLJ and PySBOL with some regularity (either with every commit to those libraries or on some timer).

[cjmyers]

All the libraries are running tests on travis every evening. They essentially do roundtrip tests using the files in this testsuite (among other tests). The travis run for this repo is just testing the tests. Namely, it uses libSBOLj to ensure the files are basically in the right place. Namely, if a file is in SBOL2_ic, that it is indeed a valid SBOL2 file that is incomplete. The invalid tests are also tested to make sure they are indeed invalid in the way they say they are. This repo does not test the libraries specifically, since the libraries are responsible for testing themselves.