Get rid of the mapboxgl.Control class

[lucaswoj]

We shouldn't require 3rd party plugins to require('mapbox-gl').Control in their module. All the code in this class could be easily moved elsewhere (i.e. map#addControl and map#removeControl methods).

ref mapbox/mapbox-gl-draw#235

[jfirebaugh]

Would we deprecate/remove existing methods like Popup#addTo? Or not try to enforce Control#addTo/Control#remove as a standard API for controls?

cc @mourner

[lucaswoj]

We could deprecate the class and alias

• Control#addTo to Map#addControl
• Control#remove to Map#removeControl

[mcwhittemore]

For the short term gl-draw has copied the Control class into its code base and removed the direct dependency.

mapbox/mapbox-gl-draw#244

[lucaswoj]

Done in #3497