Ontology: add restriction/constraint tables

A restriction is a constraint on a link between classes. Currently,
only a simple cardinal restriction is supported.
Ontology: add restrictions for each link to the jsTree data structure
Ontology: allow creation of new restrictions from context menu
Ontology: allow removal of restrictions from context menu
Ontology: add asterisk to node name if restrictions are present
Ontology: support differnt cardinality restrictions
Ontology editor: make restriction removal context menu a bit wider