Verify that the site goal is working.

Currently you could not create the site with Java 8. Unfortunately I didn't know about this. In order to avoid such an accident we will build the site on the CI server, too.
Disable parts of doclint for the site's javadoc.

This is a follow-up to e0367cd. That commit is missing to apply the doclint rules to site generation. Hence the site goal fails because of doclint issues. Now doclint is disabled for all groups but accessibility and reference for the site generation, too.
Merge pull request #1022 from stefanbirkner/travis-site

Verify that the site goal is working.