Update files in debian/* and fix Lintian warnings

Updates files in Debian folder to debhelper 9 and source format "3.0 (native)", fixes Lintian warnings.
"rtfm" is installed via debian/mintsystem.links, including manpage.
Files are moved from /usr/local/bin to /usr/bin, except for apt.
Warnings about files and dirs in /usr/local are overridden.

Remainging warnings are binary-without-manpage (can safely be ignored) and these:
E: mintsystem: init.d-script-does-not-implement-required-option etc/init.d/mintsystem start
E: mintsystem: init.d-script-does-not-implement-required-option etc/init.d/mintsystem stop
E: mintsystem: init.d-script-does-not-implement-required-option etc/init.d/mintsystem restart
E: mintsystem: init.d-script-does-not-implement-required-option etc/init.d/mintsystem force-reload

Infos: http://lintian.debian.org/tags/init.d-script-does-not-implement-required-option.html