HTTPS RESTful API for CovenantSQL

[xq262144]

Merge adapter to the main source tree, including features:

1. access database with a simple HTTP request.
2. secure request with https and custom client/server certificate.
3. query for the account balance.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (develop@2a12cbc). Click here to learn what that means.
The diff coverage is 46.66%.

@@            Coverage Diff            @@
##             develop     #74   +/-   ##
=========================================
  Coverage           ?   75.7%           
=========================================
  Files              ?     136           
  Lines              ?   11224           
  Branches           ?       0           
=========================================
  Hits               ?    8497           
  Misses             ?    1776           
  Partials           ?     951

[leventeliu]

LGTM, approve.