Added Overview panel

The overview panel is a combination of the former overcloud and plan
panels.

The assumption here is that a plan already exists; different view states
will be determined by whether an associated stack exists.

Future enhancements will include a reorganization of the templates used
and updating the mock data to simulate the creation of a Heat stack

Change-Id: I37d0943d3dbe0cb2849af82a459bc5b2af17881c