Add TimeRangeEdit and CompositeRangeWidget classes.
Integrate CompositeRangeWidget into ConversionParameterDialog.
Add QMPwidget to project.
Add files of interactive cutting feature to project.
Check whether mplayer exists in InteractiveCuttingDialog and PreviewDialog.
InteractiveCuttingDialog, PreviewDialog: check if mplayer exists when invoked.
ConversionParameterDialog: add a button to call InteractiveCuttingDialog.
InteractiveCuttingDialog: show the visual range selector.
Add "Cut" action to Edit menu.
Fix a bug that cause incorrect end-time when cutting.
Add the Cut action to context menu.
ConversionParameterDialog: set default tab to 0.
MediaPlayerWidget: add seek_and_pause() function.
InteractiveCuttingDialog: change the button text to make them less confusing.
ConversionParameterDialog: use PreviewDialog to preview cut if possible.
Add RangeWidgetBinder class.
ConversionParameterDialog: remove CompositeRangeWidget and use RangeWidgetBinder instead.
ConversionParameterDialog: fix maximum time not set.
Replace CompositeRangeWidget with RangeWidgetBinder.
Remove CompositeRangeWidget class.