add check if an ontology is imported
make user_info a function
add ability to delete a file in a repository
add destroy route to an ontology
add controller actions to delete an ontology
add button to delete an ontology to view

tooltip is not shown yet because the according bootstrap javascript is not initialized
fix source target error
fix tooltip on disabled delete button
add spec for ontology deletion
add OntologyDeleteError
improve tests on deleting an ontology
implement correct ontology deletion
Merge branch 'staging' into 398-delete_ontology_button

Conflicts:
	app/models/ontology.rb
	spec/models/ontology_spec.rb
fix syntax error in test
Merge branch 'staging' into 398-delete_ontology_button

Conflicts:
	app/views/ontologies/_menu.html.haml
Merge pull request #688 from ontohub/398-delete_ontology_button

Function to delete ontologies, which are not imported. Fixes #398.