add logic specific parsing callback

It seems appropiate (since we will we have
a lot of logic specific parsing decisions to make) to
extract this into its own callback module. This
should prevent unnecessary cluttering of
app/models/ontology/import.rb and the
OntologyParser itself.
add empty example callback for OWL.
integrate logic-specific callbacks with import.
add decisive logic-specific pre-callbacks.
Merge pull request #445 from ontohub/logic_specific_parsing_callbacks

Logic specific parsing callbacks