Test refactoring using mockito
[JENKINS-21343] Refactoring to isolate group specific logic
[JENKINS-21343] Using interface in category builder instead of specific class
[JENKINS-21343] UI now allows adding all implemented grouping rule extensions
[JENKINS-21343] Some name changes, removing useless code
[JENKINS-22415] Categorization line returns required values used by view columns
[JENKINS-19466] Fixing sort - Complete UI revamp