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
This is because a stage isn't meant to take an action, it's only meant to set values for particular variables. Deploying is an action, whereas using a stage is not.