Issue #270: Selection point by clicking on label in tools seam allowance and union. (dismine/valentina)

New issue 270: Selection point by clicking on label in tools seam allowance and union. https://bitbucket.org/valentinateam/valentina/issue/270/selection-point-by-clicking-on-label-in

Roman Telezhinskyi:

This mechanism already work for all other tools. Left just add slots for these tools.