fix(apis_metainfo): register the rootobject with reversion

This has to be done so we can follow the inheritance upwards using the
reversion extension.

apis_core/apis_metainfo/models.py

@@ -45,6 +45,7 @@
     from apis_highlighter.models import Annotation
 
 
+@reversion.register()
 class RootObject(models.Model):
     """
     The very root thing that can exist in a given ontology. Several classes inherit from it.