When a person clicks on a marker and then drags the selected marker, the marker should move

[tristen]

The way I see this playing out is:

There are two states: edit & data (drawn or imported data)

• mousedown emits a function that calls map.featuresAt. This returns the feature under the mouse and removes it from data object and put's it in the edit object.
• mousedown + drag set's a key that enables mousemove
• mousemove calculates the coordinates of the markers placement on the map and updates the new coordinates to the edit object.
• mouseup unsets the key the enables mousemove, removes the feature from the edit object and updates the data object with the new coordinates.

cc @kelvinabrokwa