Refactor TileLayer animation

[mourner]

Currently TileLayer animation logic is scattered among several files including Map.ZoomAnimation.js and Map.TouchZoom.js. We need to move this logic inside TileLayer listening to zoomanim event like how its done for all other layer types (markers, vectors, image overlays).

This will produce a better animation experience for multiple tile layers and also allow animation to fractional zooms for custom zoom-pan transitions.

[mourner]

Postpone the issue to 0.6, as it's always not a good idea to do complex refactoring as a last issue before release of a stable version (and not critical either).