JDK 8, 9 and 10 compatibility

[pesse]

For we are using JAXB in cli, there might be some additional effort needed to ensure compatibility with JDK 8, 9 and 10

[jgebal]

Should we add testing on all 3 jdk versions into Travis build matrix?

[pesse]

I'm not sure yet. Have to read/experiment around the new things.

[pesse]

Main problem at the moment is our usage of com.sun.nio.zipfs.ZipPath for HTML Coverage reporter

[pesse]

Made several tests with different java-versions installed and didn't find any issues.
We'll need to assure the compatibility with Java 8-12 by automated tests, but I'll create a separate issue for that.