Set "sketchstarted" event as when setting the first point and introducing a "sketchcreated" event.

From 2.11 sketch is usually created before starting, and is a problem not knowing when it starts (first point).

See http://osgeo-org.1560.n6.nabble.com/2-11-SketchStarted-td4550864.html and http://osgeo-org.1560.n6.nabble.com/2-11-sketchstarted-new-event-td4559041.html

Requires #314 (included as first commit 96d6884068484c179028ef4f25018be94970b129)