Support template instances in template defintion heads
Introduce ottr:hasHeadInstance
to hold the template instances of a template definition?
<asdf> a ottr:Template ;
ottr:hasParameter
[ ... ] ;
ottr:hasHeadInstance
[ ottr:templateRef <myAnnotationTemplate> ;
ottr:withValues ( ottr:none <asdf> "label" "def" 2000-01-01 ) ] .