RAT-172: Filter source code management system directories and ignore files

* Extracted information about revision control systems into an enum SourceCodeManagementSystems with tests.
* Use these SCM information when generating RAT plugin's default excludes.
* Refactored Exclusions to be Sets instead of Lists to prevent a slow RAT run on many duplicate exclusions.
* Introduced mockito and unit tests. 
* ExclusionHelperTest verifies that behaviour; AbstractRatMojo is cleaner now to only encapsulate mvn related stuff.



git-svn-id: https://svn.apache.org/repos/asf/creadur/rat/trunk@1621645 13f79535-47bb-0310-9956-ffa450edef68