[WIP] Spike of automatic package.json merging.

[rwjblue]

TODO:

• Tests
• Review
• Tests

Addresses #68

[rwjblue]

I have been able to run this successfully on a number of addons that I am updating. My workflow at the moment is basically:

ember-cli-update --ignore-conflicts
git checkout master package.json
ember-cli-update --package-json-only
git mergetool

Once I get tests in here we can consider running this automatically (or swap the flag to something like --process-package-json to run the normal update/patch then run the package.json merging code).

[kellyselden]

You can now tell git-diff-apply to ignore package.json

[kellyselden]

Brought to completion in #108