ignoreErrors fix

[MartinMystikJonas]

This is fix for my extension of ignoreErrors. I found out it does not work as expected when I used it in real-world project. This should fix it and I added test to cover it.

[ondrejmirtes]

Can you explain to me in text why do you make this change and what is your expectation?

[MartinMystikJonas]

1. ValidateIgnoredErrorsExtension was failing to validate entries with multiple messages. I extended it and I have to extract part of code to method to prevent too deep nesting.
2. Config schema did, not allowed use of reportUnmatched without path/paths so I modified it.

[ondrejmirtes]

Thank you!