flatpak: update build-manifest to retrieve dependencies without initial download phase: - dependencies are now entirely retrieved from the installation, and requirement are build from there. The source package is currently always used, and it is now possible to use PYTHON_DEP_PREINSTALL to add extra packages or use a specific version of a package. - fixed insertion of `release_elt` for dev version at the right location. - `branch` is not set anymore for stable versions. - libxslt is not added anymore as it is part of freedesktop runtime - flathub share-modules is now used for Python 2

$ORIGIN 0.0.127.in-addr.arpa.
$TTL 1D
@     IN SOA  <hostname>.<domain>. <hostname>.<domain>. (
              <date>     ; serial
              28800      ; refresh (8 hours)
              14400      ; retry (4 hours)
              2419200    ; expire (4 weeks)
              86400      ; minimum (1 day)
              )

              NS      <hostname>.<domain>.
1             PTR     <hostname>.<domain>.