User location puck for course tracking mode [squash]

[friedbunny]

Squash of #2233.

• User location puck for course tracking mode
• Tilts the user location dot and puck with the map

The puck and dot continue to be drawn as a single UIView (MGLUserLocationAnnotationView), entirely using several stacked CALayer and vectors — no images allowed here.

The pseudo-3D effects for the dot and puck while tilting are accomplished by moving the shadow offset and by vertically shifting the blue dot as pitch changes.

/cc @1ec5 @incanus @mapbox/mobile

[friedbunny]

Problems that will have to be addressed later:

• Accuracy ring does not scale properly when tilted. It's correct at the center of the map, but gets wildly inaccurate as you move the dot towards the top or bottom of the screen.
• Fake 3D isn't going to work as the pitch approaches 90º. We cap at 60º right now, though. Per User location puck for course tracking mode #2233 (comment).

[friedbunny]

Found a bug where a tilted off-screen user dot doesn't get reset when the pitch changes. Looking into a fix.

[friedbunny]

Found a bug where a tilted off-screen user dot doesn't get reset when the pitch changes. Looking into a fix.

Fixed in f502e90.

[incanus]

Checking this out.

[incanus]

Accuracy ring does not scale properly when tilted.

Refs #2186, #2045

[incanus]

This looks great and I think it's ready. Bummer about the accuracy circle, but that's bigger issues over in #2186 / having a varying meters/pixel at different points on the screen.