Add support for limiting and sorting stacks

This adds support to the stacks index call for limit, sort_keys,
sort_dir, and marker query parameters, allowing users of the API to
retrieve a subset of stacks.

With this commit, stacks are also sorted by created_at DESC by default.

blueprint pagination

Change-Id: Ib20cfae183475ff42deda82168b8b9c8d043ecd0