Working on REST API

* Added installation/running info into README.md
* Added pecan controllers for:
  * executions
  * tasks
  * workbook definitions
* Refactored controllers
* Added simple functional tests for workbooks

Implements: blueprint mistral-rest-api
Change-Id: I604b62b8b0bda5f5363b1fefedcb9ffb7447bd1d
Merge "Working on REST API"