add travis ci status.
fix typo
add integration test for resource conflict between main and test classes folder
Add integration test for pull-24 bug report.

Integration test to ensure that
https://github.com/ning/maven-duplicate-finder-plugin/pull/24 is
fixed.
Add properties for plugin configuration settings.
Report a defined message if plugin skips execution.

This fixes https://github.com/ning/maven-duplicate-finder-plugin/issues/19