Updates to support PolicyGen from frenetic

* Change switchId to SDN_Types.switchId

* Change many int64 and int32 to VInt.t (incomplete; Basu to finish)

* Expose Floyd-Warshall

* Hide edge_ports_of_switches (only used in Consistent Updates)

* Add Oasis dependency for ocaml-openflow
Merge pull request #1 from frenetic-lang/policygen

Updates to support PolicyGen from frenetic