Add JsonClientSpec

Move appropriate tests from ResourceClientSpec to JsonClientSpec
Add simple UrlUtil and spec
Add LinkHeader to http package, with tests
Pagination Part 1: The Basics
Add ClientError, ClientErrorJson and tests
Add PaginationParams, the parsed version of RawPaginationParams
Add PaginatedResult and test
Add RawPaginationParamsBinding and test
Add PaginationController and tests
Add comments before I forget what this all means
Add UrlUtil.createQueryString
Add Page to the play.client package

This provides access to relations provided by the Link header of the response.
Integrate Page into clients

JsonClient#find also now explicitly expects a JSON array.
Ensure that non-pagination params are included in Link header