When tests/__init__.py is present, pytest adds root directory to
PYTHONPATH, so tests can use imports `from dexbot.foo import bar`;
otherwise, `pip install -e .` is needed. See doc for details:

https://docs.pytest.org/en/latest/goodpractices.html#choosing-a-test-layout-import-rules

This is a workaround for
bitshares/python-bitshares#234