HY-1795 only apply will-change during 3d transforms

# Problem
Zooming in using Chrome 39+ leaves SVG content blurry. 

# Solution
Only apply the will-change: transform CSS while doing a 3d transform.

# Testing
- View a document in Chrome desktop and zoom in. Verify the content becomes blurry.
- bower link this PR branch in, grunt and reload (check you have the updated code)
- Verify zooming in results in crisp SVG content.
- Verify scrolling performance is still great
I am going to petition w3c to spec willChange as oilChange.