lib: only maintain one copy of safe_str / safe_unicode The standalone-ish nature of vcs gets a bit in the way. It already depends on some very generic Kallithea functionality. But for now, avoid code duplication, and let Kallithea use vcs functionality instead of duplicating it.

pytest >= 4.6.6, < 4.7
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, < 3.1
Sphinx >= 1.8.0, < 1.9
WebTest >= 2.0.3, < 2.1
isort == 4.3.21