introduce is? method for logictype and use it.

Conflicts:
	app/controllers/entities_controller.rb
	app/models/ontology/entities.rb
	app/views/entities/index.html.haml
fix logic.name pitfalls (by using to_s).
fix logic==nil problematic for parsing callbacks.
Merge branch '484-nil_handling_for_logics' into develop
Merge branch 'develop' into develop.ontohub.org