rpc: add getblockchaininfo and getnetworkinfo

Adds two new info query commands that take over information from
hodge-podge getinfo.

Also some new information is added:

• getblockchaininfo
  • chain: (string) current chain (main, testnet3, regtest)
  • `verificationprogress: (numeric) estimated verification progress
  • chainwork
• getnetworkinfo
  • localaddresses: (array) local addresses, from mapLocalHost (fixes #1734)