Change host provider

From an MVP perspective [Heroku](http://heroku.com/) is an easy way to deploy application and I think for a first step we should deploy with it.

Howerver there are some limitation using Heroku with Elixir/Phoenix (https://hexdocs.pm/phoenix/heroku.html#limitations):

So when the app will be used by more users we might need to find an alternative, [AWS](https://aws.amazon.com/), [DigitalOcean](https://www.digitalocean.com/), [Gigalixir](https://gigalixir.com/)?