Rather than defining more strings, reuse PACKAGE_VERSION, which is
already available.
We already use PACKAGE_VERSION for `ProductVersion` and `FileVersion` in setup.nsi.
Removes the leading 0 from the version number. The minor version, which
we had been using as the major version, is now the major version. The
revision, which we had been using as the minor version, is now the minor
version. The revision number is dropped. The build number is promoted to
being part of the version number. This also avoids issues where it was
accidentally not included in the version number.
The CLIENT_VERSION remains the same format as previous as previously,
the Major version was 0 so that was never a factor in CLIENT_VERSION.
