Modified EE-references and GEDCOM generation to use Template data structures. Added support for interface to citeproc for CSL style sheets (not ready for use yet). Modified code to work with Python3.

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/branches/geps/gep-018-evidence-style@22737 4ae1f11a-8b86-4847-b8af-ab372f36d1fd