Support passing a Template object to StackResource

The create_with_template() and update_with_template() methods of the
StackResource class previously took raw template data as an argument; this
change allows them to accept Template objects also.

Change-Id: I7af5d516d4d0c4085144ed53c962cfc6ca3c69bb
Allow a resource to be added to a template

Add a method that allows a ResourceDefinition to be inserted into an
existing template.

Change-Id: Ia418127d72d26a77d731f93cc0eb3a45d983cc82
Merge "Support passing a Template object to StackResource"
Merge "Allow a resource to be added to a template"