Plastic credit issuer

[gjermundgaraba]

A plastic credit issuer is an entity that is allowed to create credit classes and issue credits to projects.

Creating a new issuer should be governance controlled, but needs to be possible for governance to hand over control to a sub-dao/group for easier management.

Access control for creating an issuer should therefore be limited to a single address, which is set by a governance parameter. The default genesis value should be set to the governance module.

• Document the Issuer state in x/plasticcredit/spec
• Implement an "IssuerCreator" param that can be changed with a gov proposal
• Implement create issuer msg
• Implement queries for "issuer", "issuers"
• Create a smoke test that does this as well from the CLI (see scripts/tests)

Unit and integration tests everywhere!

Simulation testing will be implemented after Cosmos SDK 0.47 is out and upgraded.