Fix up phpstan

Makes possibile to ignore tasks (dereuromark#320)

* Implement ignored tasks

Adjust composer.json allow-plugins

Add test case

Fix up deprecations.

Update phpstan.neon

Update composer.json

Merge pull request dereuromark#289 from dereuromark/skip-existence-check

Allow skipping check of existence.

Fix up phpstan

Merge pull request dereuromark#285 from LordSimal/master

fix CS error introduced by last PR