data picker fixes related to point positioning.

• update the point position also in the spreadsheet every time the point is moved with the mouse on the image, i.e. retransform is called
• made the x and y columns in the data spreadsheet undo-unaware - the is no need for this since the spreadsheet is not modified manually, everything is done by creating and moving points on the image.
• fixed undo/redo for datapicker point positioning

fix #419 (closed)