feat(linux): Adjust package build for build.sh script

This change makes the necessary adjustments so that the package build
works with the new `build.sh` script. We no longer can rely on the
automatisms of debhelper. This change also adds a install target
to `build.sh`, and copies some files from the Keyman root directory
to the desktop directory because when package building we only
have access to the files in common/core/desktop. Along the same lines
it removes embedding `build-utils.h` from `build.sh`. Instead we set
the version and tier locally.