Add templates to the rails generator ala rg

Jeremy McAnally's rg plugin (http://github.com/jeremymcanally... would make a great addition to the rails generator. I'm thinking a syntax ala:

rails myapp --template my/template.rb
rails myapp --template http://example.com/template.rb

Depending on ruby2ruby doesn't seem like a good fit for Rails core, so we should come up with an alternative. Could be as simple as just having the methods declared as strings.