Hippo needs its own logo

[bacongobbler]

After merging #880, Hippo is left with no logo. Just some alt text.

Hippo's old logo was the FontAwesome Hippo logo:

https://github.com/deislabs/hippo/blob/ddc1f859c2eb27739cc1674c7fba7db7bfda9f0c/src/Web/ClientApp/src/app/components/navbar/navbar.component.html#L4

The lazy approach would be to download and serve that as the default logo. But perhaps this is a good opportunity to design a new logo for Hippo.