Added developer documentation

* Updated README file
* Updated contrib/devstack/README
* Added documentation for Devstack installation
* Added documentation for manual installation of the API and Engine services
* Added basic contributing guide
* Added extended contributing guide
* Added HACKING.rst to the root of the project
* Added development guidelines
* Sets simple Sphinx theme

Partially implements blueprint: murano-dev-doc-05

Change-Id: Ib7d7b416ccc61667ed96297555db2ef5dca9ae67
Merge "Added developer documentation"