Missing data is not elegantly error handled

[sgoggins]

Describe the bug
If a repository does not have data for one of the time periods queried, sometimes a notebook errors.

If a repository is not very active, then FREQUENTLY the reports error. This is not a problem - You can't report on data that does not exist. HOWEVER, we do need to be able to provide error handling, or an elegant message.

To Reproduce
Steps to reproduce the behavior:

1. Run augur-community-reports for python 3.8

Expected behavior

1. No Errors in ALL cases
2. Data in All Cases

Screenshots

Additional context

The same types of changes likely are required for the visualization API.