Add support for refresh tokens in OAuth, fixes T336

Summary:
- enable refresh token grant
- pass refresh token to JS app
- when oauth errors happen with user tokens, attempt to refresh
- clearing user tokens triggers UI change

Test Plan: Manually tested by manipulating token expirations in DB and watching JS logs.

Reviewers: eyedol, shadowhand

Subscribers: dkobia

Maniphest Tasks: T336

Differential Revision: https://phabricator.ushahidi.com/D165