Working on PorpNodeBuilder stuff.

* Moved InMemoryPorpNodeBuilder into the core instead of a test class,
as this is a useful builder for building....in memory!
* Corrected some PorpAddress implementation.
* InProgress/Untested: Added (re)composition just before building a
destination proxy node.
* Brought in WebApi PorpNode/Builder stuff and generalized this a bit to
begin to make it reusable beyond languageGib.