Revert "TableView: remove unused property backgroundColor"

This reverts commit 390c6fa6

.

We actually do use this to set the background color.

Change-Id: I498b3695dfb9667d8d63983576eb16ad324ea798
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>

src/controls/TableView.qml

@@ -160,6 +160,12 @@ ScrollView {
     */
     property Component rowDelegate: __style ? __style.rowDelegate : null
 
+    /*! \qmlproperty color TableView::backgroundColor
+
+        This property sets the background color of the viewport.
+        The default value is the base color of the SystemPalette. */
+    property alias backgroundColor: colorRect.color
+
     /*! This property defines a delegate to draw a header. */
     property Component headerDelegate: __style ? __style.headerDelegate : null