[pkg] Specify priority “optional” instead of the obsolete “extra” Quoting Lintian, “Since Debian Policy version 4.0.1, the priority extra has been deprecated.” So let's use “optional” instead.

missing-dep-for-interpreter make => make | build-essential | dpkg-dev (usr/*/cubicweb/skeleton/debian/rules)
embedded-javascript-library usr/share/cubicweb/cubes/shared/data/jquery.js