Example Case: > Joe writes a proposal for 50 HBD / day. He asks Alice and Bob what they think of it. Alice, being Joe's spouse, thinks it is a great proposal and immediately votes for it. Bob however thinks Joe is adding great value, but finds a daily amount of 35 HBD more reasonable. Joe wants to ask Alice to marry her and he is just a bit short on cash for the rings, so he agrees with Joe to change the daily pay to 35 HBD. With an update in a proposal UI Joe lowers the metadata `asset daily_pay` to 35 HBD. This was discussed in HiveDeveloper Biweekly 3 meeting. Updates afaict: - add `update_proposal` method including evaluator, api functions.