add tab-view for hom. DOs in logic.

Display a tab which will list all homogeneous
Distributed Ontologies which children belong to
the given logic.
fix active-tab display issue.
add test for logic-specific het. DO-fetch method.
add method to fetch logic-specific het. DOs

- add a method to fetch the logic-specific
  heterogeneous Distributed Ontologies
- Refactor duplicate code into own method (DRY)
- Use "speaking" constants instead of
  seemingly arbitrary strings.
add display of logic-specific het. DOs

This adds a new logics#show subview/partial for display of the
heterogeneous Distributed Ontologies which have at least one child
that uses the logic.