Feat/ignore mutants based on heuristics

[odinvanderlinden]

Closes #3229

[nicojs]

@odinvanderlinden Thanks for your work! As discussed, I've made some changes and am about to merge this 🎉

• I've moved the ignore bookkeeping to a separate class: IgnorerBookkeeper, and added some unit tests.
• I've rolled back the change to the prettier config. I'd happily discuss prettier changes in a separate issue, but not inside a feature PR.
• I've merged the e2e test in 'ignore-project'. I remembered that this e2e project was designed to e2e test ignorers