- added "helper lines" for quadratic curves
 * they are updated whenever any of their control points change
 * added some of the necessary "plumbing" for these
- added empty "stubs" for future boolean operations (hint, we are not there yet !)
- started tweaking code for arcs etc, similarly to what was done with quadratic/lineto etc
curves
- added minor notes about 2d shape editing
- minor experimenting with 2d shapes
- added helper.sourceParent pointing to the current instance
of shape2d so helpers "know" what shape they "belong" to
- added "translated" event handler to the shape itself (unused for now)
- added name attribute to Shape2d , defaulting to class name
- added experimental support for sourceElements to code generator:
 if this is present in the target of an operation, the generated
code uses it as the REAL target (ie, if a visual representation of
a shape was translated, what we actually mean is, the shape was translated)
- fiddling around with code generation for translation of control points
for 2d shapes (very hacky for now)
- added more notes about 2d editing
- updated grid helper (custom element & js) so that steps change
accordingly to the step attribute in the polymer element
- started adding settable "snapping"/ grid step parameters:
 * grid step number now linked to gridSettings in visual editor
 * transform controls snap attribute set based on the same setting
 * added various related on screen controls (very vasic)