Db import scripts: remove duplicated functionality / refactor

* print usage when calling das_update_database w/o params …
* remove duplicated dasmap management scripts …
  - remove ```bin/das_map``` ```bin/das_map_admin``` ```bin/das_yml2json``` and ```tools/das_mapping_db.py```
    * super-seeded by scripts that export dasmaps as mongodb json dumps and import them. P.S. this no requires ```mongoimport``` to be available
    * updated the documentation accordingly
* renamed ```das_drop_maps -> bin/das_maps_yml2json``` and ```tools/das_drop_maps.py -> tools/das_maps_yml2json.py```

fixes issue: #4129