Allow to use FindBugs filter-files with exclusions

  public File saveExcludeConfigXml() throws IOException {
	  
	// Example fix follows:
	try {
		String excludesFileLocation = project.getConfiguration().getString("sonar.findbugs.includesFilter");
		if (excludesFileLocation != null && !excludesFileLocation.isEmpty()) {
			File filter = new File(excludesFileLocation);
			if (filter.exists()) {
				return filter;
			}
		}
	} catch (NoSuchElementException e) {
		// log the exception here and proceed as before...
	}
	// End of example fix.
	  
    FindBugsFilter findBugsFilter = new FindBugsFilter();
    if (project.getExclusionPatterns() != null) {
      for (String exclusion : project.getExclusionPatterns()) {
        ClassFilter classFilter = new ClassFilter(FindbugsAntConverter.antToJavaRegexpConvertor(exclusion));
        findBugsFilter.addMatch(new Match(classFilter));
      }
    }
    return project.getFileSystem().writeToWorkingDirectory(findBugsFilter.toXml(), "findbugs-exclude.xml");
  }