Disable Trace method

We have Trace enabled, because of the apache module, which is not what Debian does by default. It is a minor issue, but we should disable it:

https://www.kb.cert.org/vuls/id/867593 https://httpd.apache.org/docs/current/en/mod/core.html#traceenable

(from redmine: created on 2016-06-16, closed on 2016-06-16)