Added 5.6.0+ compatibility fixes to wrapper.conf.
Added upstream changes to wrapper.conf.
Change default ActiveMQ version to 5.6.0.

Version 5.7.0 has a bug (bin/wrapper.jar is missing) so it should NOT be
used, at least not without proper fix. This bug is fixed in 5.8.0.

See https://issues.apache.org/jira/browse/AMQ-4199 for more info.