Changes MainWindow layout.
Merge branch 'Dev'
Comments VirtualizingPanel property.
Adds ListBox, ListBoxItem styles.  Renames List brushes.
Adds GroupBox styles to the Styles.xaml. Adds content to the empty menu items.
Adds Calendar style to the MainWindow.xaml
Adds DataGrid to  MainWindow
Adds DataGridStyle to MainWindow
Adds common style for the DataGrid  ScrollBar. Change Data. Change Layout
Adds DataGrid brushes to Styles.
Changes DataGridStyle elements style