Credit

[pgev]

As a token economy admin, I want to be able to assign tokens for my users to use within the economy so that I can increase user engagement.

Acceptance Criteria

1. An economy user can receive credit
2. Credit is usable for in-economy interactions as defined by the economy admin.
3. Credit is not redeemable.
4. A user does not require a TokenHolder contract in order to receive credit.
5. A user requires a TokenHokder contract in order to spend credits.
6. For interactions that accept credits, credits are used before tokens owned by the user/held in the TokenHolder

[benjaminbollen]

WIP PR in #144

[pgev]

WIP PR: #198

[schemar]

whoops