Don't require EVENTBRITE_OAUTH_TOKEN for local development

[gsong]

EVENTBRITE_OAUTH_TOKEN is required in order to successfully spin up the local development environment currently. We should avoid that requirement to:

1. Reduce developer setup friction.
2. Prevent distributing secrets unnecessarily.

Proposed Solution

Implement the following workflow:

isEventbriteClientInstantiated
  ? hasErrorFromEventRetrieval
    ? renderError()
    : areThereEvents
    ? renderEvents()
    : renderEmpty()
  : renderNoTokenScreen();

Address #175

[rogue0137]

hey @gsong, I'd like to take on this issue unless you have a PR I should review. Please let me know!