Refactored the PMD Maven build
- Adjusted the directory structure
- Fixed a lot of compile problems
- Fixed the maven setup
- Made PMD build with Flexmojos 7.1.0 and Apache Flex 4.13.0
- Fixed a few UnitTests

(A lot of tests are still failing, but I guess it has to be a community effort to fix all of them)
(Apache Flex and some other artifacts need to be manually deployed to your local maven repo in order for the build to work)