ImzmlTxtConverter: duplicate coordinates checking
ImzmlTxtConverter: duplicate coordinates checking

* bug fixes in WorkDir.{clean_work_dirs, drop_local_work_dir}

SpatialMetabolomics/SM_distributed,METASPACE2020/sm-engine,SpatialMetabolomics/SM_distributed,SpatialMetabolomics/SM_distributed,SpatialMetabolomics/SM_distributed,METASPACE2020/sm-engine