added dialog and functionality to call GeoObjects::mergeGeometries() from GUI
return value description for mergeGeometries, station vectors currently removed as a stn->geo converter is needed first
Refactored GEOObjects::mergeGeometries().
Merge pull request #140 from rinkk/MergeGeometriesInGUI

Added functionality to call GeoObjects::mergeGeometries() from GUI