message: Add badges to readme and update banner
diff: -![purser](https://github.com/JoinColony/purser/blob/master/.assets/purser_200.svg)
  +<div align="center">
  + <img src="/docs/img/purser_color.svg" width="600" />
  +</div>
  +<div align="center">
  + <a href="https://circleci.com/gh/JoinColony/purser">
  + <img src="https://circleci.com/gh/JoinColony/purser.svg?style=shield" />
  + </a>
  + <a href="https://greenkeeper.io/">
  + <img src="https://badges.greenkeeper.io/JoinColony/purser.svg" />
  + </a>
  + <a href="https://gitter.im/JoinColony/purser">
  + <img src="https://img.shields.io/gitter/room/TechnologyAdvice/Stardust.svg" />
  + </a>
  + <a href="https://build.colony.io/">
  + <img src="https://img.shields.io/discourse/https/build.colony.io/status.svg" />
  + </a>
  +</div>
  ## Purser
  