API.6 API: upload library blocks, choose what to add, see where they stand

POST /v1/library/uploads takes a DWG, DXF or library .json (50 MB, 20 an hour, as on the website) and answers with the blocks found; commit the ones to add with a category, license, source and the rights confirmation, or abandon. Public items wait in the same staff review as website uploads; team library items need a seat in force. Also lists the account's items with their versions and review state. Tested over HTTPS with the DXF fixture; a real DWG has not been sent through the API.