changed endpoints in metadata api 2.0

[charlottekostelic]

• added W503 (line break before binary operator) to flake8 per-file-ignores for tests
• added new base url for Metadata API 2.0
• changed get_full_bib:
  • changed response_format options to allow for MARCXML and MARC21
• changed holding_get_status to get_institution_holdings
  • changed args based on updated endpoint
• changed holding_set and holding_unset
  • added new, separate endpoints for each method
  • removed args based on changes to endpoints
• changed search_current_control_numbers to get_current_oclc_number
  • removed response_format as arg and changed default to application/json
• refactored tests based on changes to methods
• removed stale token tests for the above methods