Return version to dev

release 2.5.1

Update CHANGELOG for version 2.5.1

Merge pull request #176 from mpacer/s3_versioned_cloning

Add instructions for everywhere versions need updates to RELEASING.md

Move additional version text for response page into explicit variable

Isolate utility inside BookstoreCloneAPIHandler, add tests for utility

Add new test for s3_version_id functionality

Update docs to describe s3_version_id parameters & model values

Add s3 version cloning & update tests

Move version number back to 2.5.1.dev0

Release 2.5.0

Merge pull request #175 from mpacer/use_pathname_not_href

Fix base_url for Tornado settings (begin & end with "/")

Switch clone GET handlers & page to use relative paths for redirecting