import_logfile: Add reference_date argument
import_logfile: Add reference_date argument

Meisterschueler/ogn-python,glidernet/ogn-python,glidernet/ogn-python,glidernet/ogn-python,Meisterschueler/ogn-python,Meisterschueler/ogn-python,glidernet/ogn-python,Meisterschueler/ogn-python