R1:1febd32a765c

Don't hide columns with stats from previous age, hide columns with no data

Summary:
This does two things:

- don't fill '-' for columns where there are data from previous week
- completele hide columns if there are now new data so that noobs don't have a
55 years of history

Test Plan:
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Reviewers: vii, epriestley

Reviewed By: epriestley

CC: aran, epriestley

Differential Revision: https://secure.phabricator.com/D1750