Determine how want to include ember-cli-template-lint addon into the repo

[notmessenger]

https://github.com/rwjblue/ember-cli-template-lint

Leaning towards something "bigger" than our use of es-lint we have now and then this as well as another dependency but wrapping it all up as a single addon that encompasses all of our desired best-practices, possibly by making it all part of the style guide (by making it the addon).