tools need to be able to shadow others

[ssbarnea]

While the tool detection can easily identify all tools used inside a repository we need a way to avoid running same tasks twice.

Example one

pre-commit can also be called as standalone, from inside tox or even from a Makefile. We do not want to endup running it three times.

Implementing heuristics on this can help but I am afraid they will never be able to be perfect, so it may be better to just ignore duplicated ones via config items.