corrected threshold for quick navigation
issue #78; trying to fix thr colors
issue #65;

How will book IDs work? I think we need to implement the ID query inside
heading.html, when the settings button is pressed. For example, for
someone without JS, it would look something like
/reading-controls/?id=44
fixing "/navigation" text blinking before navigation being open on i*
trying to fix issues #68, #81