Add precommit hook for checking for merge conflicts
Add dev dep for blacken-docs
Add dev dep for pre-commit-hooks
Update all precommit hooks to use system language
Update toxfile to use new dev deps
Fix tox vs. precommit conflicts with reorder-python-imports
Add proper testenv with pytest command to run (currently trivial) tests
Update static and security envs to use variable for path identification
* Avoids transversals and errors caused by different working dirs
Add static-tests env for enforcing quality checks on test files
Update security env to include test files