Upgrade CodeClimate ESLint engine and resolve errors

[aduth]

See #3909 (comment) for additional context.

By default, CodeClimate uses an older version of ESLint than is installed in the project. It was not adhering to the expected configuration, causing both false positives and false negatives. The changes in this pull request update CodeClimate to use a version of ESLint closer to that which is installed in the application. It includes fixes to all preexisting issues.

Issues were fixed by a combination of:

• Running ESLint's automated fixer
  • npx eslint app spec --fix
• Manual review:
  • Line length exceeded -> Break to new line
  • Reference to location global -> Reference from window global window.location
  • Circular dependency -> Disable the rule
    • This is something which should be fixed, will probably be redundant with future effort toward the doc auth flow, but which would require possible significant refactoring to address now. If it's working well enough as-is, it shouldn't be a problem to keep it.

For all specific changes, note that these rules are inherited largely from Airbnb's coding standard that we follow, and are therefore largely expected.

[zachmargolis]

LGTM