Adding Mapbox vector tile basemaps

Hey @langstonsmith,

I've merged the latest master with your branch and resolved all the conflicts. There were also some inconsistencies in spacing and indentation introduced by your IDE, and it looks like there was a global search-and-replace that went awry (changing "marker" into "symbolOptions" throughout); so I reverted these. The result, squashed into one commit on top of master, is ping/langston-squashed.

I then went through and removed all the changes that weren't related to the Mapbox SDK. I noticed that you did a number of other cleanups (which were nice!), but for now I'd like to cleanly separate out just the changes that are related to this feature (we can do your other cleanups in separate commits, later). The result is ping/langston-minimal.

I'll continue working from the ping/langston-minimal branch. If you can, please continue your work by starting your own branch based on ping/langston-minimal, so it will be easier to merge our changes together.