Add documentation about heat templates for openstack-manuals

The heat developer documentation provides a reference guide for the HOT and CFN templates. This guide is very useful but is hard to use without a proper introduction to the language. A new section of the user-guide will describe how to deploy stacks with heat.

Provide a single table with all the available options for each component for openstack-manuals

We should provide a table referencing all the available options for each component. In the icehouse config ref, some options are defined in specific sections, and the user might have to go through the entire component doc to find them. It's hard to have a clear overview of which options are available. The idea of ...