Add Grand-Staff splitpoint as Configurable Item to MIDI import Dialogue
When importing a midi piano track the splitpoint between lower and upper staff is fixed to C3. In some cases this leads to unsatisfactory results. In this case it is better to forgo the splitting option and to manually split after import. It would be desireble to change the check box "split staff = checked / unchecked" in MIDI Import by a dropdown list directly indicating the split point. The top most entry should be "none", being also the default value. This is equivalent to the box unchecked.