===========================
Continue improving grease pencil for manual calibration:
- Fixed bug with local undo which was caused by not dropping
re-done nodes when pushing new undo node.
- Fixed bug with conversion grease pencil to bezier curve
(last point could be dropped away on such conversion).
- Added new mode: poly line drawing.
This mode allows to draw poly-line by clicking on
it's knots. In this mode user is allowed to pan/zoom
to new position before placing next knot.
5ddb23daec