Resolve "Restructure URL patterns"

TODO:

• How to handle /api/digital_objects/ vs. /api/digital_object_api?
• /project/dropdown_project_list/ seems to be unused. Remove?
• Document best practices (how to structure URLs)
• Make necessary changes in Rodare workflow → heliport-workflows!1 (merged)
  • /token/?
  • /user/logins/list/ → /user/login/list/
  • /gate_connection/api/gate_project/ → /api/gate/projects; also two lines below
  • /publication/api/publications/ → /api/publications/; also a couple of lines below
  • /data_source/api/data_source/ → /api/data-sources/

Closes #719 (closed)