Adding class for collection of fitted text layouts

We'll start treating them as a group for any operations (styling, cursor and
link positioning) that will require spanning across the multiple separate text
layout segments.

This commit attempts to just add/extract some of the basic classes, but doesn't
start putting them into use in the main painter classes yet.
Apply default styles to text blocks via collection

This moves over the main drawing call and default styling application to the
FittedTextLayoutCollection.