[XmlEditor] Checking IdeApp.Workspace != null before accessing it in UpdateOwnerProjects
[XmlEditor] Listening to FileAddedToProject/FileRemovedFromProject and updating OwnerProjects
Merge pull request #573 from DavidKarlas/xmlEditorAspNetMvcTestsFailing

[XmlEditor] Checking IdeApp.Workspace != null & Listening for FileAdded/RemovedToProject