Short-circuit nv.utils.windowSize logic to trigger fewer style calculations
Fix exception when mousing over dev tools in IE
Make use of requestAnimationFrame for better perf.

- Use fastdom lib to batch DOM reads and writes for jank-free (or mostly
  jank-free) rendering
- Comparable performance in non-webkit browsers (FF, IE 10+)
- Use CSS transitions to move the tooltip rather than left/top
- Re-use the tooltip container rather than creating/destroying all the
  time
- Better support for custom tooltip content generators
	- Override and return  falsey (false, null, etc) if you want to
	  use something like React, Knockout, etc to render your tooltip
	  content
- Remove styling of hidden tooltips
- Remove left/top styling of nvtooltip to avoid jumpiness when mousing
  over lines
Add fastdom to bower deps and gruntfile for karma

- Clean up a few jshint warnings