Handle module-qualification in next-clause insertion

Handle module-qualification in next-clause insertion

* sweeprolog.el (sweeprolog-definition-at-point): also return module
name when the head term is qualified.
(sweeprolog-maybe-insert-next-clause): pass module name to...
(sweeprolog-insert-clause): new argument module.
* sweeprolog-tests.el: add a couple of relevant test cases.