Integrated with travis-ci

The important changes here are

* Refactored settings layout to allow env based settings (`settings/local.py` (git ignored) `settings/travis.py` etc)

* Added `.travis.yml`. Secret keys are fetched from `settings/local.py` and encypted in to the yml file as described [here](http://about.travis-ci.org/docs/user/build-configuration/#Secure-environment-variables). Run `./encrypt.py` to automate this.

* Used `formencode` to convert the nested settings into a flat dict so that it can be easily passed to `env`. `formencode` allows us to restore the settings from the `env` vars. This is an ugly hack and I'm open to suggestions.

Please run `./encrypt.py` and update the travis status images after merging.

Thanks!