0003206: Simplify GUIWindow/GUIControl Inheritance and remove dead code (1 Viewer)

[MediaPortal-Bot]

GUIControl now has a single, small Baseclass, instead of a deep XAML like inheritence chain.
GUIWindow similarly gets rid of it's inheritence
GUIWindow exposes its GUIControls as what they are, instead of one of its baseclasses, implemented GUIControlCollection
ContextMenu reimplemented with what it actually uses (which is one single field)

Get rid of the following classes:
Core/System.Windows.Automation.Provider/IAutomationPatternProvider.cs
Core/System.Windows.Controls/Button.cs
Core/System.Windows.Controls/ButtonBase.cs
Core/System.Windows.Controls/Canvas.cs
Core/System.Windows.Controls/Control.cs
Core/System.Windows.Controls/ControlTemplate.cs
Core/System.Windows.Controls/DataTemplate.cs
Core/System.Windows.Controls/DataTemplateSelector.cs
Core/System.Windows.Controls/DockPanel.cs (used nowhere)
Core/System.Windows.Controls/Grid.cs
Core/System.Windows.Controls/HeaderedItemsControl.cs
Core/System.Windows.Controls/Image.cs
Core/System.Windows.Controls/ItemsControl.cs
Core/System.Windows.Controls/Menu.cs
Core/System.Windows.Controls/MenuBase.cs
Core/System.Windows.Controls/MenuItem.cs
Core/System.Windows.Controls/Page.cs (previous baseclass of GUIWindow)
Core/System.Windows.Controls/Panel.cs
Core/System.Windows.Controls/StackPanel.cs
Core/System.Windows/ContentControl.cs
Core/System.Windows/FrameworkElement.cs
Core/System.Windows/FrameworkTemplate.cs
Core/System.Windows/LogicalTreeHelper.cs
Core/System.Windows/SizeChangedInfo.cs
Core/System.Windows/UIElement.cs
Core/System.Windows/UIElementCollection.cs
Core/System.Windows/VisualOperations.cs
Core/System.Windows/VisualUtility.cs

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