Gossyper may react to gossyp

* Change gossyp_spec to use shoulda-matchers
* Extract models, routes, and helpers to own files
* Posting to create gossyp requires login
* Rename responses to reactions
* Gossyper may not react without a body

## [Commit by Commit Breakdown](https://github.com/tiger-swallowtails-2013/gossyp/compare/gossyper_may_respond_to_discussion)

Of particular interest may be [this commit](https://github.com/tiger-swallowtails-2013/gossyp/commit/09bfd2859a1d8aae0bf24bf4d7c02504974448da) where I use partials to render errors instead of having the same view code in two places.