Add deploy:<stage> tasks & Deploy staging by default & Refactoring

* Add `deploy:<stage>` tasks
* Deploy staging with default `deploy` task
* Rename `multistage:create_stagefiles` -> `mutistage:init`
* Remove `config/deploy/development.rb` stage file
Let's leave this configuration in. The default deploy file generated by mina comes with both a setup and deploy task. Since stages apply to any action, I think having more than one makes this clear.