This expose Sketchup::Entities#weld to the SketchUp UI via a context menu
if the user has edges selected.
A set of debugging tools is found under Extensions > Weld Debug.
Counts the number of curves found in the current context.
Assigns a unique color to each curve for easier visual identification.
Adds guide points and guide lines at the start and end of curves.
For open ended curves the start will be marked with a guide line with long dashes. The end will have dots.
For closed curves the start and end is the same point and marked with a guide line with dashes and dots.
Triggers the Check Validity of the model. (With the mac build of SketchUp this
will open the Model Info > Statistics dialog and Fix Problems must be
invoked manually.)