More Plugin renovation work

- Use a result collector for reporting. This ultimately will allow saving the results of a
  duplicate check run (and therefore further processing e.g. with CI plugins)
- Remove the notion of "current project" from the exceptions configuration. That never really worked
  and is not necessary. Add an ArtifactFileResolver which is able to deal with conflicts of the
  current project.
- add new flag 'preferLocal' to determine whether artifacts found in the local repository or
  folders of a local project from a multi-module build shoul be preferred when doing conflict
  resolution
- Fix a bug in the PluginLog, now uses the right log levels
- code formatting