Support for setting font type and size

This is the simplest mockup/idea I could come up with. Having a popover based design without modal dialogs (to see updates in the document in real time) would be much better though.

Screencast_da_22-02-2019_14_19_42

My idea would be to have the EPUB viewer widget accessible from this class and then get/set font using these functions: GNOME/libgepub!5 (merged)