Add option for MPA owners to disable collateral bidding

[abitmore]

User Story

As a MPA owner I'd like that there is an option to disable collateral bidding for my MPAs.

Specifications:

• new disable_collateral_bidding bit in asset flags and issuers_permissions
  • unable to set before hard fork
  • unable to set on UIAs, but can be set on PMs (although useless)
  • common logic about issuer permissions (if permission is forfeited, unable to update flag, unable to enable permission if supply is non-zero, etc)
• if set in flags, unable to bid collateral
• when newly configured via asset_update_operation, cancel all collateral bids
• at hard fork time, cancel all collateral bids of asset which already disabled collateral bidding (due to old bug)

Impacts
Describe which portion(s) of BitShares Core may be impacted by your request. Please tick at least one box.

• API (the application programming interface)
• Build (the build process or something prior to compiled code)
• CLI (the command line wallet)
• Deployment (the deployment process after building such as Docker, Travis, etc.)
• DEX (the Decentralized EXchange, market engine, etc.)
• P2P (the peer-to-peer network for transaction/block propagation)
• Performance (system or user efficiency, etc.)
• Protocol (the blockchain logic, consensus, validation, etc.)
• Security (the security of system or user data, etc.)
• UX (the User Experience)
• Other (please add below)

Additional Context (optional)
Add any other context about your request here.

CORE TEAM TASK LIST

• Evaluate / Prioritize Feature Request
• Refine User Stories / Requirements
• Define Test Cases
• Design / Develop Solution
• Perform QA/Testing
• Update Documentation

[froooze]

What is wrong with bidding on debt ?

[abitmore]

Done via #2504.