BarMapGUI and TempoMapGUI remember skin
adding TempoBarMapView

a version of BarMapView that converts to time/seconds internally, and
keeps track of tempo changes
UChainGUI use TempoBarMapView

can now track tempo changes. Also tweaking gui to look more coherent
startTimeMode popupmenus should not focus
adding durationMode to UChainGUI

can be \duration, \endTime and \endBar, changing the duration display
accordingly