Transitions WIP

I updated the basic browser support matrix, and removed the crazy-old webkit workaround. I also removed the old code for prefixing transitioned properties, because it was over-simplistic. 

It would be nice to add that back in, with a more robust approach, but I couldn't figure out a way to make it happen. Help, @chriseppstein or @scottdavis ?

I did update the tests, so they fail currently, but should pass if you get it working. I also updated `$transitionable-prefixed-values` so it shows a list of values and the prefixes that should be applied to them.