introduce initial, unit tested google cloud platform element set

This is the minimum needed for my codelab (compute engine is the first and only cloud product supported, and only part of GCE at that) but I think it also builds a decent starting point for cloud polymer components. I defined a naming convention for elements and files to hopefully avoid a proliferation of confusing and inconsistent names used across the many cloud products.
Is there only one progress indicator at any one time? My feeling is you should declare the tag and show and/hide it based on the state:
   
 <progress id="prog" hidden?="{state == 'init' || .state == 'started'}}"></progress>