Set the color of GroupBox via TemplateBinding

Added a setter for Background and BorderBrush, so you can set the color of the groupbox without overriding the whole style.
added .NET45 version of System.Windows.Interactivity
added .NET45 project and updated solution
updated nuspec file
updated references to use .NET 4 version of System.Windows.Interactivity
updated build script
Added release notes for upcoming 0.10.1 release
whoops i missed a sentence
removing commented out code
SelectedItem set to white foreground

The selected item should have a white foreground to match other controls as groupboxes.
introduced AccentSelectedColorBrush key to replace usages of White inside ListBox/ListView
removed commented-out code
updated release notes
Merge branch 'master' of https://github.com/MahApps/MahApps.Metro