Removed Mapbox Light and MapBox Warden. Added new styles for GMaps Gray Roadmap. Updated basemap dropdown: now we show 4 elements per column. Changed copy for initial state of the dropdown
Merge branch '2.0' of github.com:CartoDB/cartodb20 into 2.0

* '2.0' of github.com:CartoDB/cartodb20:
  Added thin to Gemfile development group