WIP: Git based app blueprints

Extends `ember new'`s `--blueprint` option to accept git remotes in either `git@someservice.com:app-blueprint-test.git` or `https://someservice.com/trek/app-blueprint-test.git` style git remote urls.

Not a huge fan of how this is tested, but short of mocking I can't think of any way to truly test without  doing an actual  `git clone`