Remove source folders used for tests

Instead, I've added four JAR files that contain
the original content of the four source folders,
respectively. A new rule extracts them to
a temporary folder each from which a custom
ClassLoader can be build.
ClassesOnClasspath optionally scans JARs
ClassesOnClasspath optionally scans wildcard dirs
Remove logging to get rid of dependencies
Support for JUnit 3 and @RunWith