Add SWRL support

[cmungall]

Currently funowl doesn't support SWRL rules. Here is an example SWRL rule in ofn:

Prefix(:=<http://purl.obolibrary.org/obo/ro.owl/>)
Prefix(obo:=<http://purl.obolibrary.org/obo/>)
Prefix(owl:=<http://www.w3.org/2002/07/owl#>)
Prefix(rdf:=<http://www.w3.org/1999/02/22-rdf-syntax-ns#>)
Prefix(rdfs:=<http://www.w3.org/2000/01/rdf-schema#>)
Prefix(swrl:=<http://www.w3.org/2003/11/swrl#>)
Prefix(swrla:=<http://swrl.stanford.edu/ontologies/3.3/swrla.owl#>)


Ontology(<http://purl.obolibrary.org/obo/ro.owl>
DLSafeRule(Body(ObjectPropertyAtom(obo:RO_0002180 Variable(<urn:swrl#w>) Variable(<urn:swrl#p>)) ClassAtom(obo:BFO_0000015 Variable(<urn:swrl#w>)) ClassAtom(obo:BFO_0000015 Variable(<urn:swrl#p>)))Head(ObjectPropertyAtom(obo:RO_0002018 Variable(<urn:swrl#w>) Variable(<urn:swrl#p>))))
)

for reference, this is how it looks in omn:

http://purl.obolibrary.org/obo/RO_0002180>(?w, ?p), <http://purl.obolibrary.org/obo/BFO_0000015>(?w), <http://purl.obolibrary.org/obo/BFO_0000015>(?p) -> <http://purl.obolibrary.org/obo/RO_0002018>(?w, ?p)

and the very ugly rdf/xml:

   <rdf:Description>
        <rdf:type rdf:resource="http://www.w3.org/2003/11/swrl#Imp"/>
        <swrl:body>
            <rdf:Description>
                <rdf:type rdf:resource="http://www.w3.org/2003/11/swrl#AtomList"/>
                <rdf:first>
                    <rdf:Description>
                        <rdf:type rdf:resource="http://www.w3.org/2003/11/swrl#IndividualPropertyAtom"/>
                        <swrl:propertyPredicate rdf:resource="http://purl.obolibrary.org/obo/RO_0002180"/>
                        <swrl:argument1 rdf:resource="urn:swrl#w"/>
                        <swrl:argument2 rdf:resource="urn:swrl#p"/>
                    </rdf:Description>
                </rdf:first>
                <rdf:rest>
                    <rdf:Description>
                        <rdf:type rdf:resource="http://www.w3.org/2003/11/swrl#AtomList"/>
                        <rdf:first>
                            <rdf:Description>
                                <rdf:type rdf:resource="http://www.w3.org/2003/11/swrl#ClassAtom"/>
                                <swrl:classPredicate rdf:resource="http://purl.obolibrary.org/obo/BFO_0000015"/>
                                <swrl:argument1 rdf:resource="urn:swrl#w"/>
                            </rdf:Description>
                        </rdf:first>
                        <rdf:rest>
                            <rdf:Description>
                                <rdf:type rdf:resource="http://www.w3.org/2003/11/swrl#AtomList"/>
                                <rdf:first>
                                    <rdf:Description>
                                        <rdf:type rdf:resource="http://www.w3.org/2003/11/swrl#ClassAtom"/>
                                        <swrl:classPredicate rdf:resource="http://purl.obolibrary.org/obo/BFO_0000015"/>
                                        <swrl:argument1 rdf:resource="urn:swrl#p"/>
                                    </rdf:Description>
                                </rdf:first>
                                <rdf:rest rdf:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#nil"/>
                            </rdf:Description>
                        </rdf:rest>
                    </rdf:Description>
                </rdf:rest>
            </rdf:Description>
        </swrl:body>
        <swrl:head>
            <rdf:Description>
                <rdf:type rdf:resource="http://www.w3.org/2003/11/swrl#AtomList"/>
                <rdf:first>
                    <rdf:Description>
                        <rdf:type rdf:resource="http://www.w3.org/2003/11/swrl#IndividualPropertyAtom"/>
                        <swrl:propertyPredicate rdf:resource="http://purl.obolibrary.org/obo/RO_0002018"/>
                        <swrl:argument1 rdf:resource="urn:swrl#w"/>
                        <swrl:argument2 rdf:resource="urn:swrl#p"/>
                    </rdf:Description>
                </rdf:first>
                <rdf:rest rdf:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#nil"/>
            </rdf:Description>
        </swrl:head>