SpecObject.publish() should add spec to default WebRegistry

[andyk]

Note the below framing of this feature assumes #250 is either already done or this could be done as part of #250.

Publishing a spec via my_spec.publish() should be a thin wrapper for the following:

reg = get the default WebRegistry (which depends on whether local test flag is set)
my_spec.to_registry(reg)

Once identifiers are hashes, this should never fail since identifiers of two different specs will be unique.

Then we would need a different mechanism for allowing human readable names of specs (to make sharing easier/more intuitive). Perhaps something akin to git branches.