Fixed some bugs in the RunconfigToDistribution task:

- versions supplied in the run config was not taken into account
  when searching for the right artifacts, causing it to always
  take the last version available;
- made the NonTestProjectFileFilter a little more efficient,
  fixes (closed) issue #384;
- added proper log-levels to log messages and a flag to make the
  task less verbose.
Made the cleaning of the output directory optional:

- added cleanOutputDir option to disable the behavior of deleting
  the contents of the output directory;
- made the cleaning of the output directory recursive in order to
  remove it, even when it contains a nested directory structure;
- some other minor cleanups.