[bitshares/bitshares-core] Update all asset-related API’s to support asset symbol as parameter (#1051)

**User Story**
As an API user I want to use asset symbols directly for all APIs. Some APIs support asset symbols, e.g. `get_ticker`, but others don’t support, e.g. `get_market_history`.

**Impacts**
Describe which portion(s) of BitShares Core may be impacted by your request. Please tick at least one box.
– [x] 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)**
https://bitsharestalk.org/index.php?topic=26699.0

## CORE TEAM TASK LIST
– [ ] Evaluate / Prioritize Feature Request
– [ ] Refine User Stories / Requirements
– [ ] Define Test Cases
– [ ] Design / Develop Solution
– [ ] Perform QA/Testing
– [ ] Update Documentation

This post was last modified on June 14, 2018, 12:26 am