[Cin] New native Tracer plugin checked into GIT

[Andrea paz]

Nice new plugin; thank you. GG is a great coder.
If I understand correctly it is like the normal mask tool but that
traces the contours as the "magic wand" of GIMP. So we're talking
selection masks, not "matte"; right?
It's not very clear to me how the "Scale" works.
I have to request some additions (if feasible, of course):
- The first time you click on RMB, could you replace the default point
already present? This way, I should not delete it manually each time
or move it with LMB to the desired position. Obviously it should only
work for the first click, so I don't know if it's possible to do it.
- Could more outlines be added? Like the sketcher plugin that has an
upper section where to create new curves (outline[?]) and a lower
section where to create the points of these curves (ie the section
already present in Tracer).
- Could you move the entire mask with ALT + DRAG or something like that?

I only did a few quick tests, so I probably talked without knowing the
plugin. Sorry for the imprecision.