PyLoxi 1.3 work

Reviewer: @andi-bigswitch

These changes add support for more OpenFlow 1.1+ classes. Instructions and meter bands are added in their own modules. The end result is PyLoxi can now serialize/deserialize OF 1.3 flow-mods.

The major set of classes remaining are the table features. There's also a problem with the way LOXI represents the set-field action (it has an opaque payload instead of an OXM member). We're getting into territory where I'm not sure the LOXI core completely supports 1.3 so there may be work to do there.