Break contract "preparation" into phases reflecting the usual workflow

[shonfeder]

Generally, our contracting preparation goes something like this:

1. There is a template lawyers have prepared for the purpose
2. On the basis of the template, someone from within the organization prepares a draft with some basic known information about the party and context (e.g., the parties name, their job title and description).
3. The other party supplies additional information (e.g., their address, list of prior inventions).
4. The other party reviews the contract, requesting any changes they see feet (negotiation / correction).
5. The other party executes.
6. Someone from within the org-executes.

I think it could improve our process, and open up some avenues for for more structured gathering and representation of data to represent (at least some of) these distinct phases in the tooling. (E.g., perhaps we want to start tracking the "state" of a contract through some meta-data?)

Possible commands would be

• themis-contract prepare foo: (1) -> (3) -- Given a template id foo, this would produce a partially configured contract, after collecting from the preparer additional information needed, including the destination repository and directory where the external party with interact with the contract. This could also post the partial configuration there, and notify the party via email.
• themis-contract fill foo: (3) -> (4) -- Would prompt the external party to supply all the missing information, then present the filled contract for review. It could also prompt them to either accept and sign or make changes.
• themis-contract ammend foo: (4) -- Could be useful for structuring the process of making changes.

The existing sign command would pick up from there.