Util function for querying which classes are interconnected

[pablo-de-andres]

Related to #443, I think something along these lines could prove quite useful:

from osp.core.ontology.oclass_restriction import RTYPE, Restriction
def get_ontology_connections(subject, object):
    for ax in subject.axioms:
        if not isinstance(ax, Restriction) or \
           ax.rtype == RTYPE.ATTRIBUTE_RESTRICTION:
            continue
        if object.is_subclas_of(ax.target):  # Alternatively if object == ax.target:
            yield ax.relationship