Now we have difference between KisFilter::factoryConfguration() and
* KisFilter::factoryConfguration() creates an empty configuration
object of a proper C++ type. This object should be filled by fromXML()
right after this call.
* KisFilter::defaultConfiguration() calls factoryConfiguration() and
fill it with default values at the state how they should look in
This split is needed, because new versions of Krita may introduce
options not available in older saves configs. In such cases, Krita
should be able to recognize if the config is the "old" one, and
doesn't have new parameters.