Template repository support

It would be nice, if grunt-init would support downloading templates from a central repository (npmjs for example), when the template isn't available locally.

This would mean:
- Correctly labeling (i.e. grunt-init-template) all available packages in npmjs
- Implementing a method of searching with npm, when the template isn't available locally
- If only one template is returned from that search, install the package to ~/.grunt-init (after asking the user)
- Use that template