* Add JavaDoc build badge
* Add dependency to upgradetool to fix remaining JavaDoc error
* Fail JavaDoc build on JavaDoc warnings/errors
* Upgrade maven-javadoc-plugin to fix it failures even if there are no warnings/errors
* Enable legacyMode to workaround JPMS issues in newer maven-javadoc-plugin versions
Signed-off-by: Wouter Born <github@maindrain.net>