decrease Unused color category priority below every other one except Other
fixed: SyntaxConstructClassifier grays out records, DU and DU cases even though they are used somewhere
move Unused symbols classifier logic to Core project (not all tests pass yet)
fix Colorizer tests, add some for Unused category
add more tests for Unused color category
Merge pull request #552 from vasily-kirichenko/fix-class-graying

fixed: class name declaration grayed out even though there's default constructor usage