Moves non-lwt code out of lwt submodule

The code that I've moved out converts between our SDN abstraction layer
and OpenFlow 1.0/1.3. None of it is Lwt-specific and can be used by
async too.

frenetic builds unchanged with this refactoring, as it is all internal.
Merge branch 'abstraction-layer-common-elements' into header

Conflicts:
	_tags
	lib/openflow.mllib
	myocamlbuild.ml
	setup.ml

Resolved by running "oasis setup".