first-run: Add basic installer and packages for Debian distros.
This adds the installer to allow Debian-based distros to run and a basic set of packages needed to at least allow kdesrc-build to successfully run --initial-setup, as tested under a Docker image of debian 9. This will still miss the dependencies required to fully make it through any kind of reasonable KDE software build. In particular even if I included the list of Qt modules that Debian 9 stable has available, they are too old for current git-based applications. But other modules are probably needed and still missing (suggestions accepted! :). So there's still more to do here, which is why the bug remains open. See issue #15 CCBUG:402901