move config of input values tracking into das maps

* add input_values section to DAS Maps: dbs.yml, sitedb2.yml [?sitedb?] in services/cms_maps
    - TODO: services/maps?
* outputing the values into mongodb import scripts:
  - (yml) map_reader
  - das_drop_maps
  - tools/das_mapping_db
* reading the config: DASMapping().inputvalues_uris()
* modify input values tracker accordingly

fixes issue #4111
minor refactoring
fix naming
apply changes to both maps and cms_maps; use dbs3 instead dbs

* also update services/maps dir
* moved input_vals section from dbs.yml to dbs3.yml, as the APIs used to load values are from DBS3