ember new command to create project scaffolding

This seems to be working pretty well for me. I'd appreciate a code review before you pull it in. I was hoping I could keep it simpler than this, but I really didn't want to "just overwrite" any files for fear of a bad user experience. This quickly became the most complex CLI app I've ever had to write in node. I have some plans for extracting a lot of this code into helpers/cli framework, but here it is for now.

To try it out:

1. Create an empty directory to hold your new app
2. Run `ember new` to create the scaffold (optionally pass `--name <custom-name>` to not use the name of the current directory)
3. Run `npm install`
4. Run `ember server` to spin up a server and hit http://localhost:8000
3. Bask in the glory that is your new app

Note that the namespace/modulePrefix becomes whatever name you gave your app (defaults to the name of the current directory).

It should also prompt before overwriting any files.

What do you think?