Augmenting for issue 112 ontology link graph

This pull request should take care of the following issues:

- #112 
- #226 
- #84

This particularly includes the following parts:

- Display graph for Ontologies
- Allow setting a depth for the graph
- Allow switching to Import-Hierarchy graph (dependent on kind *import_or_view*)
- Display graph with links defined by the ontology for distributed ontologies