When printing an ad inserter widget area, wrap the area with a container

[rnagle]

Wrapping the widget area with a div (or maybe an aside) is something we'll almost certainly need in order to properly style any inserted objects.

The markup for the wrapper should include, at minimum, a class to indicate the index of the widget area. For example, scaip-1, scaip-2, etc.

[benlk]

For shortcodes using the automatically-inserted [scaip number=2] syntax, it will now wrap the output widgets in <aside class="scaip scaip-2"></aside>. Widgets were already wrapped in per-widget asides, but now the whole stack will be wrapped.