Added the possibility to change the units in the change parcel dimension page

With the Change Parcel Dimension action from the Parcel Selection page it was already possible to change measurements of a parcel, but not the pieces.

The functionality has been expanded to now as well support changing the pieces of a parcel in both directions.

Different to a measurement change (which is in background a production order), is a change in pieces posted as either a positive or negative adjustment.

See the parcel selection documenation for further reference: https://docs.acadon.de/products/timber/en-US/timber/parcel-selection.html