Update Stylesheet (specifically typeface, replacing SF Pro)

[justinjiangrws]

Is your feature request related to a problem? Please describe.
SF Pro, the typeface, is proprietary and Apple restricts its use to only Apple devices.

Describe the solution you'd like
I've gone ahead and change the stylesheet accordingly using Avenir Next, Helvetica Neue, and Archivo Black/Narrow.

See the changes here: https://www.figma.com/file/iUS5LdAnuTKVei88QwPPCH/Bay-Area-Pandemic-Dashboard-PanDa-by-Bay-Area-Brigades?node-id=1023%3A715

Additional context
Let me know if text/font files cannot be found, but otherwise think it's a pretty straightforward change.

[kengoy]

@justinjiangrws The change has been made. Please review if the expected font is being used on different devices.