Merge branch 'master' of https://github.com/Dirkster99/Avalondock

Update README.md

https://github.com/Dirkster99/AvalonDock/issues/11

The fixed order of the two lines (in two places) in Xceed.Wpf.AvalonDock.DockingManager.cs as shown below.

_layoutItems.Add( layoutItem );
ApplyStyleToLayoutItem( layoutItem );

Added support for nl-BE

xceedsoftware/wpftoolkit#1424

https://github.com/xceedsoftware/wpftoolkit/pull/1187/files

AvalonDock Fixed some null reference exceptions #1170

https://github.com/xceedsoftware/wpftoolkit/pull/1170/files

xceedsoftware/wpftoolkit#1138

Update README.md

increased minor minor version to 3.4.0.4

Added comments in themes/Generic.xaml of VS2013 theme to document imp…

…lementation of overlay buttons.

Update README.md