Spotbugs Maven Plugin 4.7.3.2

• Resolve #549 auxclasspath regression introduced from 4.7.3.1 release
• Bump base-parent usage to 38 resolving recursive issue with m2e (or more generally with maven itself) introduced from 4.7.3.1 release
• Add new integration tests to test that files are not left open (verify-clean) and test to ensure we do not reintroduce auxclasspath issue (check-no-missing-classes).
• Resolve #236 - inner classes links fixed