replace tile fade animation

[incanus]

See discussion here. Basically this is a switch from doing a reveal animation on each tile to doing a fade animation on the tile renderer's sublayers. This has the same desired tile fade effect, but solves #96 and also allows a potential future toggling setting on the renderer if this behavior is not desired, as opposed to checking from each tile image.

[vyskocil]

I tried the patch but I hadn't experienced much improvement, perhaps you did other tweaks to have better results ?
I experienced the best results when I replace kCATransitionReveal with kCATransitionFade in RMTileImage.m and set mapView.contents.tileDepth to 2. With these changes the new tiles are blended like if it there is 'mipmapping' in action.

[incanus]

Setting tileDepth isn't an option when you use alpha-transparent tiles.

When I revert my commit, I get the flash. When I add it, there is only a fade. Here's a video in simulator for each:

• flash without patch
• no flash with patch

I made both within a few seconds of each other changing only this commit.

[incanus]

I'm going to close this pull request as:

1. I didn't branch properly and this is tracking mapbox/master, which is way too much.
2. My fix here is only noticeable on MBTiles tile sources. I'm going to be doing more work here for both local & web-based sources to try to improve the fade animations where possible. I'll open separate issues for that.