ember 2.18.2

[GavinJoyce]

Part of https://github.com/ebryn/ember-model/issues/462

This PR upgrades ember-model to use Ember 2.18.2. In order to minimise changes, I've tried to replicate the previous container logic with getOwner and setOwner.

TODO:

• [x] 5 last five remaining tests (might be related to https://github.com/emberjs/ember.js/pull/15871)
• [x] rebase and confirm 🍏
• [x] confirm that this works for our own app in dev
• [x] confirm that this works for our own app in production
• [x] rename any remaining container variables to owner

[GavinJoyce]

I cut a custom build based on our Intercom fork and it seems to work well in dev: