Detect addons by package.json keywords

[dwickern]

Ember-cli detects addons based on the keywords field in package.json (source):

  "keywords": [
    "ember-addon"
  ],

We currently look for a .ember-cli file in the directory but not all addons have it. For example ember-code-snippet.

[Turbo87]

Checking the keywords would certainly be the better option, but it is also a little more complex to code so I used .ember-cli as a good-enough heuristic. Feel free to adjust this if you think it's worth it.