Removed #4986
Revert #3552
New 'flex' support

http://dev.w3.org/csswg/css-flexbox/
https://developer.mozilla.org/en-US/docs/Web/Guide/CSS/Flexible_boxes
fab css
Convert tabs to spaces
set overflow-x: hidden on Firefox only

workaround crazy Firefox-only behavior when selecting newlines

closes #3549
Conflicts:
	IPython/html/static/style/style.min.css
fab css
Merge pull request #5051 from jdfreder/ff-hscroll2

FF Fix: code cell missing hscroll (2)