Pass all properties when creating midpoints and vertices, close #846

[drewbo]

Updated the createMidpoint and createVertex to take a first parameter GeoJSON feature instead of an id. This allows passing properties down to the created points. This also updates all the calls to those functions (I think) and the necessary tests (plus two extra for adding userProperties)

[awulkan]

I have also created an implementation for this, which works with the latest version of Mapbox Draw, and can be seen here:
https://github.com/awulkan/mapbox-gl-draw/tree/vertex-midpoint-properties

I will not submit a pull request though since it appears that @drewbo has already submitted one. I didn't know that this pull request existed until I was about to submit my own.

Please consider adding this functionality from either my or drewbo's code. It's a highly necessary feature for anyone that needs custom styling. In my situation I need to be able to hide vertices and midpoints so that our users don't think they can drag/reshape certain polygons.