Apply styling to segments within layout collection

This first commit moves towards applying segment styling (from sub-spans, links,
etc) when working against multiple layouts. This isn't wired in yet, doesn't
do actual styling, but gets the iteration in place properly for selecting
the ranges and layouts to work against.
Merge styles together on segment before applying

A range can potentially have multiple styles applied to it, so apply all of
them starting from the default style before actually setting the style.