Merged changes from the branch 'dev_v22'
Run tests - pass
Added one more argument validation to FileDialogCommand ctor
Removed an unimplemented by MS property RestoreDirectory from FileDialogCommand
Added more properties to FileDialogCommand with handlers in OpenFileCommand and SaveFileCommand that allow better setting up standard dialogs
Added missing XML comments to these three new commands
Added one more commom property to FileDialogCommand class and it's processing to OpenFileCommand and SaveFileCommand classes
Added license headers to three new source files