There was a mistake in the logic used to choose between the Comparison
and Two Content layouts: if one column contained only non-text (an image
or a table) and the other contained only text, the Comparison layout was
chosen instead of the desired Two Content layout.
This commit fixes that logic:
> If either column contains text followed by non-text, use Comparison.
Otherwise, use Two Content.
It also adds a test asserting this behaviour.
