Debian: use autotools_dev and xz compression, update Stand.-Ver., update...

... to debhelper 9

I thought it might not be important but it's still included in recent releases on Sid, so I guess I revert that. By the way the rules file of 7.1.0 has some other changes too, maybe you just want to use their script? http://ftp.debian.org/debian/pool/main/m/mkvtoolnix/mkvtoolnix_7.1.0-1.debian.tar.xz