Typography Controls

[NateEaton]

I've made a first pass at adding a broader set of controls for font face and size, line spacing, margins, etc. See the new header icon in reading view. It replaces the font size items in the overflow menu.

I'm still working on fine-tuning the width settings but I'm leaving that till I start work on the tablet layout changes.

Build #391 is the latest build and although it's mainly focused on internal code improvements it also includes the earlier PR with the typography control changes.

Feedback welcome.