GladeDataModel: fix editor issues
- Editor looses current editing row if eprop_data->editing_row is cleared in clear_view()
- Get critical assert if editing_row is not cleared (glade:148136): Gtk-CRITICAL **: 21:21:12.702: gtk_cell_layout_get_cells: assertion 'GTK_IS_CELL_LAYOUT (cell_layout)' failed
- String columns do not seems to get updated
Ideally we should not recreate everything when changing a value