Add helper related generators

[tansongyang]

This was my first go at a *-addon generator. Like *-test, it also required copying some files from the ember.js repo.

[chriskrycho]

Thanks, @tansongyang! You're just knocking these out like crazy! To fix the lint error:

/home/travis/build/typed-ember/ember-cli-typescript/blueprints/helper-test/index.js
  4:34  error  "ember-cli-is-package-missing" is extraneous  node/no-extraneous-require

Just add "ember-cli-is-package-missing" to the package.json. Easiest way I've been doing it is just yarn add ember-cli-is-package-missing.

[chriskrycho]

Oh, and as a quick related note: you should be able to catch this kind of lint problem by doing yarn run lint:js (defined here in package.json). That'll drop your personal cycle time since we don't have to wait on Travis for it.

[chriskrycho]

@dfreeman is this kind of re-export going to work/compile properly as TypeScript? I think the answer we got to was yes, everything works except things in app/ in the root of an addon but wanted to confirm.

[dfreeman]

I think we want these to just be .js files (since this is going to land in app/ in the root of the addon) — I can open a PR to update the blueprints we have in place