Enable the importation of Mapbox drawings

 - Given a Mapbox project, we can now draw shapes and locations by
   freehand and our Shareabouts map will mimic these shapes in our
   Shareabouts project.

 - Some additional items to be completed (in a new issue):
   - Include marker images for point shapes
   - Verify that line shapes are working correctly
   - Include description under the title in the clickable popup

 Closes #2