Make it easier to view template URLs "directly"

It's not easy to view a raw template directly. i.e. to view/discover URLs like:

https://ampstart-iframes.firebaseapp.com/templates/travel/travel.amp#amp=1

It would be useful to expose these URLs in some way to make it easier to:

- Link directly to these templates. (I don't think this is possible right now--without looking at the source, you can only link to a category like "Art & Design".)
- Quickly see how the template looks at screen sizes other than the preset ones.
- View the source via devtools or similar to see how a particular feature is implemented. (This is possible now, but since the resource is iframed it can be difficult to find.)

Suggestion: add a button next to "Download" that opens the template in a new window.


Locate the template preview's existing Download control and inspect how the iframe and template URL are generated. Add a neighboring control that opens the template directly in a new window, then verify that the direct URL supports linking, alternate viewport sizes, and easier source inspection.

Written by the indexing model from the issue text.