suggestion to add GRAPHENE_BLOCKCHAIN_NAME to config

**User Story**
As a graphene fork and bitshares blockchain developer I want the name of the blockchain to be added to config so that client programs i write can display the info to their users.

Global var can be added at https://github.com/bitshares/bitshares-core/blob/master/libraries/chain/include/graphene/chain/config.hpp#L26 and displayed initially just in the `info` wallet call at:
https://github.com/bitshares/bitshares-core/blob/master/libraries/wallet/wallet.cpp#L548

I think this will be also be displayed automatically at https://github.com/bitshares/bitshares-core/blob/master/libraries/app/database_api.cpp#L623

Another spot can be as an initial title banner when witness node is started. Currently when the chain is new a banner "Welcome to graphene" is displayed. Displaying the blockchain name when chain is not new can be a good idea.

Looking for comments.

**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)
- [x] 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.)
- [x] UX (the User Experience)
- [ ] Other (please add below)

Start in libraries/chain/include/graphene/chain/config.hpp at the referenced global configuration area, then inspect the info wallet call in libraries/wallet/wallet.cpp and the database_api.cpp entry point. Review the witness startup banner as an additional possible display location. Confirm the intended scope before making the blockchain name consistently visible in the selected API and CLI outputs.

Written by the indexing model from the issue text.