ParserStatistics: remove all getter methods for individual sets/fields/etc

They are never used anywhere.
ParserStatistics: add a MatcherStats class; add predefined class sets
Replace ParserStatistics visit methods with new MatcherStats class

Works very well, much cleaner.
ParserStatistics: code style, some logic fixes

With sets in particular.
Write a custom AssertJ assert for ParserStatistics; start to use it

Soooo much better thant testing against .toString()!
Add AssertJ dependency! Oops...
Remove all .toString() tests on parser stats, replace with StatsAssert
Simplify StatsAssert