[HV-838] Make resolved type cache not static.
HV-838 Doing some polishing

* Using a more generic name for the helper
* Removing helper parameter from some methods where it is not needed
* Removing ExecutableElement#overrides() in favour of ExecutableElementHelper#overrides() to simplify usage
HV-838 Adding Brent to copyright.txt
HV-842 Make xmlInputFactory in XmlParserHelper an instance variable
Adding unused import checkstyle rule and fixing existing violations