Better support of decimals change in ctkCoordinatesWidget

The number of decimals can be changed from the ctkDoubleSpinBox
directly. Let's make sure the new number of decimals is not overwritten
by the coordinates widget.
Merge branch 'ctkcoordinateswidget-decimals'

* ctkcoordinateswidget-decimals:
  Better support of decimals change in ctkCoordinatesWidget