Need to tweak responsive behaviors for 2-col-stacked regions

[meganem]

Right now, when someone makes a complex layout using the 2-col-stacked regions, they are not obeying the responsive rules as we had hoped. For example:

First column:
[span6] [span6]
[span6] [span6]

Second column: [span12] [span12]

Basically until we hit the smallest breakpoint, things are just getting squished, because our rules are only taking into consideration the outer wrapper span6's and not the ones inside each column.

I am going to custom fix this for Admin Guide (which has this layout on the homepage), but it's something we should have a fix in for in general, along with some of the other regions needing tweaks.