Dashboard date and partial data warnings

[Bruno Bowden]

Summary

Two UI changes:

1. "Data up to Dec 20" as a warning that the data might be stale. As data is updated, then it would switch to "Data up to Dec 24". NOTE: there needs to be separate dates for the national and global stats as they may be different see #1724.
2. Warning at bottom of the page: "Data may be incomplete for the current day or week" - this is copied from the WHO Dashboard:

Checklist:

• Searched the existing issues to ensure you are not creating a duplicate.
• Followed the Contributor Guidelines.