mathjax iframe injection
Merge branch 'develop' into feature/mathjax

Conflicts:
	js/views/reader_view.js
Merge branch 'develop' into feature/mathjax

Conflicts:
	js/views/reader_view.js
added mathjax call
loading mathjax on demand
Implement iframe content, script, and reading system object injection.
Merge branch 'feature/iframe_injection' into feature/mathjax

Conflicts:
	js/views/reader_view.js
Pass mathjax url to iframe loader.
Inject mathjax script
Disable old mathjax injector function for now.
Don't re-use the same iframe element for reflowable layouts.
Instead destroy and create one every spine item change.
This fixes an issue in where MathJax does not reinitialize on spine item document changes.
Inject reading system object before writing to the iframe DOM.
Remove previous attempt at reading system injection.
Merge branch 'feature/iframe_injection' into feature/mathjax

Conflicts:
	js/views/iframe_loader.js
Disable the remove parent inline script injection.
Disabling absolute URI base href hack (loses compatibility for IE<11)
Fixes #66, CSS column pagination empty/blank pages when body spacing (padding/border)
Additional tweak for #66, min/max diff influences columnised scrollWidth (try accessible_epub first page with bottom HR)
Should address issue #68 (center spread corrupts left/right sequences)
addresses #57
Merge branch 'develop' into feature/mathjax

Conflicts:
	js/views/reflowable_view.js