* [core] Add interface to get image from sprite atlas
* [tests] Add tests for Map::getImage
* [ios, macos] WIP: get MGLImage for name from style
* [ios, macos] Fixed -imageForName:
Convert from sprite images to platform images using the existing encodePNG() function, which is also used for printing. Allow -imageForName: to return nil without an assertion failure. Added a basic test.
So far, we didn't properly disable layers that are outside the zoom range. This means that we rendered layers that should not have been rendered, albeit we didn't make any attempt to load tiles for those layers. However, when zooming in/out, existing tiles might already have been loaded in the source which continued to be rendered. In most cases they weren't actually visible because either the matrices weren't updated, or the clip IDs weren't set so that they would be "rendered" off-screen and clipped completely. In any case, we did way too much work.
add outlinepattern shader class to relevant files
add outlinepattern code to painter_fill.cpp
add outlinepattern code to fill_bucket
refactor painter_fill, fix tests
fix merge conflicts and setDepthSublayer
update render test to no antialiasing so travis will be happy
