Update class and project metadata with impact info

[blushi]

As part of #64, we've defined how the primary impact, measured co-benefits and project benefits (not measured) should be stored in the credit class metadata as well as project-specific descriptions for those impact in the project metadata. But we are still missing the data for updating the existing credit classes/projects (in particular knowing which impact are measured or not). Once we have that, we can work on this issue which should include:

• adding the updated metadata to the ops folder
• preparing txs for those updates and coordinating signing/broadcasting