[REST CLIENT] yields data pages with requests context

[rudolfix]

Tell us what you do here

1. guesses the single entity endpoints from the path when creating resources
2. NOTE: data_selector is JSONPath now, backward compatile with string names
3. yielded page data is an extended list with requests context
4. all tests are passing

[burnash]

@rudolfix I'm merging it, let's address the trailing slash in a follow-up request.