[docs] add readthedocs to the project

[florianlenz]

Feature / Issue

Since we plan to grow as an organisation (we will hire more mobile dev's) we need a good way to document the project. The documentation will contain:

• JSDoc directly taken form the source code (We want to avoid the need for copying over JS doc to the sphinx files)
• Documentation that explain architecture / hight level stuff (not directly related to source code)

We will use http://readthedocs.io/ to host our documentation. It uses sphinx to generate documentation. There is a plugin called sphinx js which allow us to pull the javascript code directly from the js files instead of copying JSDoc over manually. There is need for writing a custom build logic since we probably need to strip the flow annotation's from the source code. After the build process succeed the files need to be pushed to read the docs via there api.

Acceptance criteria

• Add read the docs and sphinx to the project
• Create docker container for custom build logic
  • keep in mind that there is need for authentication in the build container if it's called
  • keep in mind that we need logging in case something escalates in the docker container. Papertrail is a fantastic service for logging.