Create setup mix task for phoenix apps

[joaomdmoura]

Create a Mix task that will setup the state field into the desired module, set the initial state as default on the database, and fill up the initial code for the developer.

[axelson]

If anyone is thinking of picking this up, I think igniter would be a good library to use because it is built to support code patching: https://elixirforum.com/t/igniter-a-code-generation-and-project-patching-framework/64181