Improve SignatureTests

* Explore the freebase graph deeper but not as wider, so the total output is smaller and the test runs faster, but we explore more different areas of the graph
* Include quotations output in tests, so we can see if we're generating weird or unperformant expressions. This way we also test if the signature changed and if it didn't crash while generating the expressions in the same test, saving overall time
Merge pull request #232 from ovatsus/master

Improve SignatureTests