Improvements to scaffold plugin

As I spoke on gitter room:
I was thinking about few features:
* downloading templates from `github` ( I've done my first, mini plugin to do that https://github.com/charafau/sbt-giter8-scaffold-fetcher )
* extend plugin to class generation. i.e. one could specify model like `scaffold ` . then plugin could generate more detailed view - similar to `rake` in `rails` for generating model, view and controller

thanks!