Add mto_id to ticker data

[syalon]

User Story

In some cases, we need to directly use the market_ticker_object object to obtain ticker data in batches. The current ticker api can only obtain a single trading pair. It is not necessary to add a new api, so we simply add mto_id to the current ticker data.

Updated by @abitmore: related to issue #1937.

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)
• UI (the user 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)

[abitmore]

Please elaborate (motivation and rationale).

[abitmore]

Thanks. I'll merge this as a temporary solution.