fix init.d script and other stuff

This pull request has less changes then https://github.com/linuxmint/mintsystem/pull/13

This will update the Debian files to the new debhelper format and it'll fix the following Lintian tags:
```
E: mintsystem source: source-contains-unsafe-symlink usr/bin/rtfm
W: mintsystem source: debian-rules-missing-recommended-target build-indep
W: mintsystem source: debian-rules-missing-recommended-target build-arch
W: mintsystem source: binary-arch-rules-but-pkg-is-arch-indep
W: mintsystem source: ancient-standards-version 3.7.2 (current is 3.9.5)
E: mintsystem: copyright-should-refer-to-common-license-file-for-gpl
W: mintsystem: copyright-without-copyright-notice
W: mintsystem: extended-description-line-too-long
E: mintsystem: file-in-usr-local usr/local/bin/mint-md5sum
W: mintsystem: file-in-unusual-dir usr/local/bin/mint-md5sum
E: mintsystem: prerm-calls-updaterc.d mintsystem
E: mintsystem: postrm-does-not-call-updaterc.d-for-init.d-script etc/init.d/mintsystem
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
E: mintsystem: python-script-but-no-python-dep usr/lib/linuxmint/mintSystem/mint-adjust.py
E: mintsystem: python-script-but-no-python-dep usr/local/bin/apt
W: mintsystem: binary-without-manpage usr/bin/rtfm
W: mintsystem: executable-not-elf-or-script usr/local/bin/mint-md5sum
W: mintsystem: init.d-script-does-not-source-init-functions etc/init.d/mintsystem
```
<br>
The remaining files in /usr/local/bin should be moved to /usr/bin or to a different location outside of /usr/local and installed to /usr/local/bin via update-alternatives. But for this pull request I kept them where they are. Same for the stuff in /usr/lib.
Looks like it also has to depend on zenity because of mint-md5sum.