Added "ember-addon" config to package.json

- Includes use of the "after" hook to specify that ember-cli-gzip should
  be executed after broccoli-asset-rev
- Creates support for using broccoli-asset-rev (fingerprinting)
  alongside gzipping (this is a smart default)
Merge pull request #3 from jdjkelly/feature/default_to_after_broccoli_asset_rev

Added "ember-addon" config to package.json