Odi tweaks

Hi Ben

I've made a few tweaks here:

* remove `.ruby-version` and set up ruby version and gemset in the Gemfile
* allow an optional logo on the Submit page (could probably use some design magic)
* redirect _/_ to something more useful for our users (configurable in _config/config.yml_)
Right now the app is structured to be repo agnostic (e.g., it can be used for multiple repos). Perhaps just a generic root redirect URL (which could be set to a repo)?