Be more graceful when Google sheets is not configured

[Mr0grog]

Enough people have hit confusion around the Google sheets configuration that we really should clean this up. The current status is that it’s “optional” in the sense that certain routes are expected not to work and the app won’t crash if not configured. But we log config errors in that case and people get confused. So:

• Methods that retrieve data from sheets should return early with nice errors if not configured (server/sheet-data.js)

• The UI should not have an “assigned pages” view or support the assigned pages routes when sheets is not configured. This should probably be a config var named something like SHOW_ASSIGNED_PAGES for the front-end that is calculated based on the Google Sheets env vars. (server/configuration.js)

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed in seven days if no further activity occurs. If it should not be closed, please comment! Thank you for your contributions.

[Mr0grog]

This has been a barrier for some contributors, so I think it’s important to track and fix.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed in seven days if no further activity occurs. If it should not be closed, please comment! Thank you for your contributions.

[lightandluck]

Added never-stale label

[Mr0grog]

The sheets-related methods still need to return early if not configured, but we removed the assigned pages view and all the associated bits (the most painful part people were running into) in #395 and #398.