Add AssertionException, specialize pprint
diff --git a/ide/CellModel.cpp b/ide/CellModel.cpp
index 8271c87..0aa29bb 100644
--- a/ide/CellModel.cpp
+++ b/ide/CellModel.cpp
@@ -147,6 +147,11 @@
     addCell(Cell(code, result));
 }
 
+void CellModel::insertCellBefore(int index)
+{
+    insertRow(index);
+}
+
 void CellModel::announceCellChange(Cell *cell, int role)
 {
     // TODO: Optimize