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_)
IIRC, `.ruby-version` is used by `rbenv` to set up the execution environment, while placing the ruby version in the Gemfile simply errors out if that version is not met, no?