Implementation of a Heat stacks UI.

This change implements a UI to launch, manage and delete Heat stacks.

The launch screens are implemented with a set of chained forms where
the second form is dynamically built from the template in the first step.

A significant portion of this change was derived from
the work Dan Radez <dradez@redhat.com> did on thermal:
https://github.com/steveb/heat-horizon

UX flow revisions and basic test cases by Gabriel Hurley.

Implements blueprint: heat-ui

Change-Id: I294e93bed6da9dd3553e8b4a6a1c09b7c165a555