timeline: rewrote ripple deleting into an undoable command that takes place

after the gaps are made and cleaned

Results in more reliable ripple delete behavior.

Also fixes bug that would cause gaps that were cleaned and then restored in an
undo to crash when selected.

app/widget/timelinewidget/tool/pointer.cpp

@@ -219,7 +219,7 @@ void TimelineWidget::PointerTool::MouseReleaseInternal(TimelineViewMouseEvent *e
   bool inserting = (event->GetModifiers() & Qt::ControlModifier);
 
   // If there are any blocks to remove, remove them
-  parent()->DeleteSelectedInternal(blocks_to_temp_remove, false, false, inserting, command);
+  parent()->DeleteSelectedInternal(blocks_to_temp_remove, false, false, command);
 
   if (inserting) {
     // Make room to insert clips to