Workers share Map Label Builder

Consolidate writing channel to an MVar shared by the worker threads,
building up the map of pending write traffic there.

Use a single MVar () to signal the writer thread to wake so it doesn't
busy loop.

Handle additional envelope field in ROUTER socket. Call it mystery'
because it's not clear where it goes.
Fix vault build
Organize contents update by origin

Fix Label vs Origin glitch in the vault binary. There was a reason
those were guarded with newtypes.
Restore strongly typed Origin and Label
Rename vault harness to UtilityProgram

As with ingestd -> IngestDaemon, this is so we can navigate using
ctags properly.