Disable scrolling for `overflow: hidden` elements
Merge pull request #1226 from mrmr1993/noScrollOverflowHidden

Disable scrolling for `overflow: hidden` elements
Prune unnecessary stuff in ensureScrollChange.
Smooth scrolling, first functional.
Smooth scrolling, adjust duration for longer scrolls.
Smooth scrolling, refactor scroller.
Smooth scrolling; stop at edge of activated element.
Smooth scrolling; tidy up for PR.
Merge branch 'smooth-scrolling' of github.com:smblott-github/vimium into smooth-scrolling

Conflicts:
	content_scripts/scroller.coffee
Smooth scrolling; fix merge.