adding attributes: order of attributes

[dieuska]

Research how the order of attributes is handled; check if this can be improved

[dieuska]

At the moment it looks like the original attributes are stored alfabetically; and afterwards the brdr_fields are added

[dieuska]

although we have included the possibility to load extra attributes in brdr, we are not going further on this topic to keep a ordering for qgis.. This has to be handled in (py)qgis itself, by f.e making a full copy of a layer