Add tests for the 2.1 fixtures

[ksclarke]

Have learned there are IIIF presentation fixtures so I need to add tests for them, fixing any issues along the way.

[ksclarke]

Fixtures that represent a full-manifest have been added and handled with the exception of the following ones:

• Fixture-25
• Fixture-36
• Fixture-38
• Fixture-39
• Fixture-40 (Not sure I want to support this one)
• Fixture-41