Create tests for all endpoints

[nicholascar]

Use a local file vocab containing Collections to test all endpoints for:

• [x] Index page
• [x] About page
• [ ] SPARQL page
• [ ] SPARQL endpoint
• [x] Vocabulary
• [ ] Collection
• [x] Concept
• [x] Container of Vocabs

[nicholascar]

Most test implemented in https://github.com/RDFLib/VocPrez/blob/master/tests/test_endpoints.py. Others to be implemented as needed