Update Icon for Viewer Site to Viewer Icon

[joewheaton]

@philipbaileynar maybe you can teach me how to do this by adding a documentation page to https://developer.riverscapes.net on how to do this?

[philipbaileynar]

I can't recall whether we can change favicon. Might need to talk to Michael.

[joewheaton]

Can we elevate this please @philipbaileynar?

[philipbaileynar]

Main logo is updated.

favicon is a known issue across all sites that use our Gatsby theme.