LevelCelView: Rename QActions of Add Frame to Append Frame

This patch renames all QActions instances in MainWindow from Add Frame to Ap
Frame, this way it's more clearer for the user, since "Insert" option is
already adding frames, "Add" right now seems to be too ambiguous.

source/levelcelview.cpp

@@ -1586,7 +1586,7 @@ void LevelCelView::ShowContextMenu(const QPoint &pos)
     QObject::connect(&action0, SIGNAL(triggered()), mw, SLOT(actionInsertFrame_triggered()));
     frameMenu.addAction(&action0);
 
-    QAction action1("Add", this);
+    QAction action1("Append", this);
     action1.setToolTip("Add new frames at the end");
     QObject::connect(&action1, SIGNAL(triggered()), mw, SLOT(actionAddFrame_triggered()));
     frameMenu.addAction(&action1);
@@ -1622,7 +1622,7 @@ void LevelCelView::ShowContextMenu(const QPoint &pos)
     QObject::connect(&action5, SIGNAL(triggered()), mw, SLOT(actionInsertSubtile_triggered()));
     subtileMenu.addAction(&action5);
 
-    QAction action6("Add", this);
+    QAction action6("Append", this);
     action6.setToolTip("Add new subtiles at the end");
     QObject::connect(&action6, SIGNAL(triggered()), mw, SLOT(actionAddSubtile_triggered()));
     subtileMenu.addAction(&action6);
@@ -1661,7 +1661,7 @@ void LevelCelView::ShowContextMenu(const QPoint &pos)
     QObject::connect(&action10, SIGNAL(triggered()), mw, SLOT(actionInsertTile_triggered()));
     tileMenu.addAction(&action10);
 
-    QAction action11("Add", this);
+    QAction action11("Append", this);
     action11.setToolTip("Add new tiles at the end");
     QObject::connect(&action11, SIGNAL(triggered()), mw, SLOT(actionAddTile_triggered()));
     tileMenu.addAction(&action11);