mermaidr 1.2.8

• Ensure column observers appears for all methods and data in mermaid_get_project_data()
• Add columns num_sample_units, num_active_sample_units, suggested_citation,
  and bbox to results returned from all project endpoint functions
  (mermaid_get_projects(), mermaid_get_my_projects(), mermaid_search_projects(),
  mermaid_search_my_projects())
• Add vignette on importing CoralNet data to MERMAID