Fix bug where QuickDialogTableView does not use appearance from root element

If the appearance had a nil value for tableGroupedBackgroundColor, the backgroundColor was not being set in `applyAppearanceForRoot:`

- Added default values for the properties tableBackgroundColor and tableGroupedBackgroundColor in `QAppearance`

- Modified `applyAppearanceForRoot:` to handle setting the background colour for both plain and grouped UITableViews.

Applications that are setting the backgroundColor in `setQuickDialogTableView:` can move the call to `viewWillAppear:` or use the rootElement's appearance as shown in the Sample application's LoginController