First cut at debhelper 7 support

First cut at debhelper 7 support

* Update to debhelper compatibility level V7.
  - Use dh where possible in debian/rules.
  - Use dh_lintian to install Lintian overrides.
  - Eliminate the configure target and do all the work in build.
  - Do more in the install target and less in binary, matching the
    default command stacks in dh.
  - Use a debian/clean configuration file to let dh clean do more of the
    work rather than using rm commands in debian/rules.