Include fix 14125
(issue https://avalondock.codeplex.com/workitem/15949)
Implement fix 13626

'IsHidden' and 'IsAutoHidden' have been added as dependency properties to 'LayoutAnchorableItem' so that they can be bound to a view model. The change to 'LayoutDocumentTabItem' prevents an exception in some scenarios when moving tabs.
Include Patch 13111

Related to the discussion here: http://avalondock.codeplex.com/discussions/400843

This adds a property to the LayoutGroup class named 'CacheTabsContent', defaults to false but when set to true, it uses the class TabContent from: http://www.codeproject.com/Articles/460989/WPF-TabControl-Turning-Off-Tab-Virtualization to cache to content of the tabcontrol that holds the LayoutDocumentControl/LayoutAnchorableControl.

I didnt test much yet, but would like to have feedback if a solution like that would be OK to be integrated into AvalonDock.

This patch modifies all existing themes to integrate the functionality.