Add directional current location UX/UI icon

[nvkelso]

For all the icon sets: tangrams/bubble-wrap#250 (comment)

Paired up with mapzen/ios#333, add a new icon that shows both the current location dot ( • ) and adds a triangle that can orient towards direction of view, more like ( • )>

For v1 we'd need to whitespace buffer the non-triangle sides so the rotation point is
still centered on the ( • ) portion of the icon.

We're looking at adding support for this as part of mapzen/ios#391.

[tallytalwar]

Just a note, our friends at streetcomplete have had a shot at this, refer screen shots here: tangrams/tangram-es#1712

[nvkelso]

Looks nice!