Add Diagram (and more details) to Templates Overview

**WIP. Don't merge yet** -- Needs revision and feedback :)

- Added diagrams for each template, indicate how it looks and where the "features" will appear
- Indicate which template group(s) use each template
- Provide up to 3 example uses of each template (link to JS file in Spice repo) 

@russellholt any feedback on this so far?

I think it's a little redundant to indicate which templates are for tiles/detail given their names, except for "icon" and "record". Perhaps icon should be "icon_item"?

cc// @jagtalon @jdorweiler @mwmiller