db: refactor to clarify that we always invoke SA create_all with checkfirst=False create_all(checkfirst=True) would skip creating tables that already exist, potentially leaving them with wrong schema. We are strict and want a successful create_all to leave all the tables in a fully known state. We thus want it to fail if any tables already are present. Existing tables should not silently be accepted.

pytest >= 4.6.6, < 5.5
pytest-sugar >= 0.9.2, < 0.10
pytest-benchmark >= 3.2.2, < 3.3
pytest-localserver >= 0.5.0, < 0.6
mock >= 3.0.0, < 4.1
Sphinx >= 1.8.0, < 3.1
WebTest >= 2.0.6, < 2.1
isort == 4.3.21
pyflakes == 2.2.0