update files in debian/*, move binary-indep. files to /usr/share

Move files to /usr/share and eliminate as many Lintian errors as possible.
I've now managed to get rid of all warnings except the missing manpage stuff. And /usr/local/bin/apt is now installed via postinst script.
To remain compatibility, a symbolic link from /usr/share to /usr/lib is added, and could be removed, if all Mint packages are edited to be installed in /usr/share and look for their stuff there.

Please let me know if there are any problems, before just closing the pull request. I could revert problematic changes.