moves the ember dep in the package-manager package.json into optionalDependencies

[CNDW]

having ember in the dependencies forces a npm install of this repo to have a duplicate install of ember. If someone is installing ember/ember-data via the components shim library, their package.json will have to look something like this

    "components-ember": "https://github.com/components/ember/archive/2.4.2.tar.gz",
    "components-ember-data": "https://github.com/components/ember-data/archive/2.4.0.tar.gz",
    "ember": "https://github.com/emberjs/ember.js/archive/v2.4.2.tar.gz"

[bmac]

Thanks @CNDW