Hardware accelerate on iOS!

[aseemk]

iOS Mobile Safari hardware accelerates CSS transitions on CSS transforms and opacity. We should experiment with one or both of these instead of using <canvas> like we do currently.

The good news is that the code already has support for using CSS transforms (used in Chrome), and one-frame-long CSS transitions on those transforms exactly for this purpose. It used to cause tile flickering, so we turned it off, but that tile flickering may be the same bug we fixed in the v0.8.9 update!

Either way, we should also use CSS transitions on opacity to blend the tiles. We will likely have to use the same one-frame length hack since we remove/re-add tiles from the DOM each frame.