Add primitives signature/endorsement, update input/msg cmds.

This creates primitives for message signatures and input "endorsements". The term signature is overloaded, and is more appropriately applied to message signing than input "signing". The proper metaphor for input singing is endorsement, as in the endorsement of a bank draft, so that is now used for `input-sign` (which may be better as `input-endorse`) and `input-verify`.

This also further refines GSL templates, although there is work remaining. Finally, a test is enabled for the deterministic `input-sign` scenario.