Handle unavailable years

[TaiWilkin]

Overview

Certain geographies may not be available for all years. In those cases, we should indicate which years are available for the geography, and prevent users from selecting a year if no selected geographies have data available for it.

Additional Context

See mockups here

[rajadain]

When selecting a year for which data is not available for all regions:

The unavailable region is still mentioned in the Questions page, even though it will be excluded in the final result:

Wonder if we can have some sort of disabled / grayed out treatment to indicate that here.