* debian/upstream-signing-key.asc: Add keys from upstream.
   * Rename: debian/upstream-signing-key.asc -> debian/upstream/signing-key.asc
   * debian/watch: Make use of the signing key from upstream.
   * debian/upstream-signing-key.asc: Add keys from upstream.
   * Rename: debian/upstream-signing-key.asc -> debian/upstream/signing-key.asc
   * debian/watch: Make use of the signing key from upstream.