Allow querying of assets with filters

**User Story**
As a `developer` I want `to get assets matching certain criterias without having to query all and filter locally` so that `the network and processing load is reduced, for client and server`.

Possible filters (may combine as pleases):
- asset type (uia, bitasset, prediction market, anything else?)
- simple regex search for symbol (only define * as any)
- *X: any asset that ends with X
- YYYY.*: any asset under the namespace YYYY, or starts with YYYY. (equivalent)
- YY*: any asset starting with YY (includes also YYYY.X)
- *YY*: any asset that has YY somewhere in the symbol
- *.BTC: All assets that ends with .BTC (should return OPEN.BTC, BRIDGE.BTC etc, but NOT OPEN.BBTC)
- list of asset issuers (nice to have, would facilitate loading of trusted issuers)
- list of asset holders (nice to have, would speed up loading all assets for one user)

**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)**
Facilitate loading and filtering from UI, and reduce load on nodes.

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