For each example, allow the user to see and copy the markup that creates it

[prushforth]

This relates to the "Make the <mapml-viewer> self-perpetuating" epic. For these examples, it would be ideal to give the viewer the ability to copy/paste the markup that creates the example, similar to how the GeoGratis directory pages' templates work for individual layers, except it would be ideal to use a standard method/technique and not have to do too much work to obtain that result.