All enabled tests are now true unit tests with no external dependencies; new `requirements.txt` file in `test/` that installs testing requirements (`pytest`, `pytest-mock`, etc.); and `run-tests.sh` now has an extra step that installs these

SSA-6727: reorganization and reworking; this commit fixes setup.py. don't make dev. don't try to walk the tree.

system since I figure that's on its way out the door)