Issue 248 patch - Update JMESPaths

[digitaldogsbody]

This PR updates the JMESPath constants for both IIIF Presentation v2 and v3 to fix some potential issues.

Presentation v2:

Problem: Non-Image services could be picked up by the selector.
Fix: Add a filter clause to make sure the @context block of the service is for an Image API version. The reason for using this field is per Presentation 2.1.1 section 5.4: "A reference to the Image API context document MUST be included", so on a valid Manifest it will be present.
Playgrounds:

1. Current code, picking up Search service in third canvas: http://play.jmespath.org/?u=926ccfd3-0b1f-43b2-b431-b9c9b3bdbf93
2. Fixed code, picking up Image services for Canvas 1+2, and not the Search service in Canvas 3: http://play.jmespath.org/?u=cccfd941-f3c7-418f-844f-44b85ddee0f4

Presentation v3:

Problem 1: Current selector only works if all services are v3 (i.e with id and type). Having even a single v2 service (with @type) causes the whole selector to fail on the contains conditional and return a single null for the entire manifest (not just the one block).
Problem 2: Assuming above fixed, current selector only returns id for the service, meaning it misses v2 services with @id.
Fix 1: Push both type and @type into a hash, and use the not_null function to select the one that actually exists, and then assign it to type, then use this for the conditional selection of only Image services.
Fix 2: Repeat the same push-to-hash/not_null trick with id and @id, ensuring that id will then have the value from whichever one exists.
Playgrounds: (n.b. each of these has a third canvas which should never get a service_id as it only contains a Search service)

1. Current code, working with only v3 services: https://play.jmespath.org/?u=1a017e4f-064e-48fb-b469-1cbfac6f8b71
2. Current code, failing to null when one v2 service exists: https://play.jmespath.org/?u=07998489-58d0-47cb-b4ba-5b7dd5278431
3. Fixed code, working with both v2 and v3 services and returning consistent output regardless of whether @ is present in input keys or not: https://play.jmespath.org/?u=b0d17ada-8b30-4f8f-a2cd-9f8296b90b78

[DiegoPino]

Amazing @digitaldogsbody thanks so much. Merging!