Lintian complains about package-contains-cmake-private-file a lot

[James Henstridge]

Lintian complains about where cmake-extras installs its modules, as described here:

  https://lintian.debian.org/tags/package-contains-cmake-private-file.html
  https://wiki.debian.org/CMake

For our Find*.cmake modules, it sounds like we could instead install them to the following location instead without any change to dependent projects:

  /usr/share/cmake/${name}/${name}Config.cmake

This is discussed in more detail here:

  https://cmake.org/cmake/help/v3.0/command/find_package.html

Things are a bit more complicated for the other files like EnableCoverageReport.cmake that are usually pulled in directly via include(). One option would be to change it to find_package(CoverageReport), and leave a stub EnableCoverageReport.cmake that makes the find_package() call and emits a warning as a transition strategy.

If we make this change, we should also get rid of the need to rebuild cmake-extras every time a new version of cmake hits the archive too.