Create multiple implementations of the wallet interface

[sKudryashov]

Preface: The "wallet API" is a multi-token API. It has one interface that exports a few functions. Then there are multiple implementations of the interface for individual coins:

• generate an address (from seed)
• check balance (get unspent outputs for an address)
• get all pending transactions concerning an address or list of addresses (deposits, later deposits and withdrawals)
• check status of transaction by transaction id
  and wallet API, exposes an HTTP, JSON interface, that can be used by other applications

Issue:
For bitcoin create multiple implementations of the interface
so we have a list of

• coins, implementations
  and can instantiate an instance of the interface/implementation for a specific coin
  then access the instantiated interfaces through an http json api or via CLI

One implementation for bitcoin uses the "scanning wallet" (but has to connect to a bctd node)
one uses blockchain.info api, etc

The command line tool can call the json http request directly, on the running server

The "wallet api" only needs to support bitcoin and skycoin for now (two coins) and one or two implementation for bitcoin (scanning wallet and querying blockchain.info)

[nutmix]

@sKudryashov Hi, the sigma team would like to take this task. How do we contact you to clarify the requirements?

[sKudryashov]

Hi, @nutmix, I have already started working on it. Not sure how to mark it as "in progress" in this issue tracker though.

[gz-c]

I assigned it to @sKudryashov