Remove custom styles from ace.js

The overflow-y:scroll property seems to make the .ace_scroller section prone to losing sync with the gutter.
Add modernize and test for touch events, style .ace_scroller accordingly

Since overflow-y:scroll was causing problems with .ace_scroller on desktop, but is necessary for mobile, we need to only target touch-enabled devices. This isn't 100%, but should prevent undesirable behavior on desktop.
Merge branch 'scrolling-cursor-fix'