InvalidCastException when repository set to project (#467)

System.InvalidCastException: Unable to cast object of type 'System.String' to type 'SoftwareIdeasModeler.Core.Projecting.IProjectItem'.

at SoftwareIdeasModeler.Dialogs.Pickers.RepositoryPickerForm.repositoryTree_AfterSelect(Object sender, NodeEventArgs e)

at SoftwareIdeasModeler.Controls.FastTree.FastTree.OnAfterSelect(NodeEventArgs e)

at SoftwareIdeasModeler.Controls.FastTree.FastTree.treePanel_MouseDown(Object sender, MouseEventArgs e)

at System.Windows.Forms.Control.OnMouseDown(MouseEventArgs e)

at System.Windows.Forms.Control.WmMouseDown(Message& m, MouseButtons button, Int32 clicks)

at System.Windows.Forms.Control.WndProc(Message& m)

at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

OF=SoftwareIdeasModeler.MainForm

LastCmd=SoftwareIdeasModeler.Core.Commands.CombinedCreateCommand

OF=DockablePanel.Controls.DockablePanel.FloatingForm

OF=SoftwareIdeasModeler.Forms.StartForm

OF=SoftwareIdeasModeler.Forms.ProjectForm

OF=SoftwareIdeasModeler.Forms.EditorForm

OF=SoftwareIdeasModeler.Dialogs.Properties.ItemPropertiesForm

OF=SoftwareIdeasModeler.Dialogs.Pickers.RepositoryPickerForm