Automatic filtering down to only shared states should be togglable

[nmdefries]

"Total across shared states" behavior is confusing. The alert that plots are only showing should be WAY higher on the page and brought to the user's attention (red, bolded, etc).

The user should be able to turn on/off "Total across shared states" behavior to throw away states not available at all time points.

Related: Nick Reich has previously requested that the state filter logic be changed to not be so strict. At the moment, we throw out a state even if it's only missing for one week.