Bundle map dependencies to work offline

We should bundle everything [in the map template](https://github.com/mapbox/mbview/blob/f2f6ace6abfa38725da58e90cff882e80dffb2f5/views/map.ejs#L7-L9) so mbview can work totally offline. Even if we don't have basemap tiles, visualizing something would be better than nothing.
