Add methods to highlight letters on nt hover
Remove unneeded count method
Add defaultHighlight/Normalize methods

I've found it nice to default methods for when I want to wrap them with
something else. Also, we no longer override the highlight methods if the user
sets one of them.
Scale letters when zooming in

We decrease the size of the zoomed highlight letters. This should help prevent
them from running off the plotting window. The scaling is not very good right
now as it will have the letter smaller than the normal font but it's a start.