New setup screen for blog installation.

fixes #3072
- Change router to handle /ember/setup/
- Adjust doSignup to also handle setup
- Adjust tests and add new where necessary
- Add setup controller, setup validation, setup route
- Adjust casper emberSetup to handle new setup


**Note: ** In order for this to look correct we need an update of Ghost-UI (`vertical` needs to align vertically, `button-add` should be green (currently overridden by `input[type=submit]`))

/cc @PaulAdamDavis
Can this `ajax` work be offloaded into the `DS`?