Add prettier to blueprint

[bmish]

Implements this RFC: https://github.com/emberjs/rfcs/blob/master/text/0628-prettier.md (emberjs/rfcs#628)

Changes included:

• Installs prettier dev dependencies (package.json)
• Updates lint scripts (package.json)
• Adds plugin:prettier/recommended to .eslintrc.js
• Creates new file .prettierrc.js
• Adds .prettierrc.js to Node files override in .eslintrc.js
• Adds .eslintcache to .eslintiginore
• Creates new file .prettierignore (duplicate of .eslintignore)
• Fixes prettier violations in blueprints and test fixtures

TODO:

• update tests
• manually test this
• ensure ember-cli generated code has no prettier violations
• update ember generate to run lint:fix to fix prettier violations in external blueprints? (RFC section)
• manually update ember blueprints (components, controllers, etc) to fix prettier violations

[rwjblue]

update ember generate to run lint:fix to fix prettier violations in external blueprints? (RFC section)

We can tackle this separately I think.

[rwjblue]

Thank you @bmish!