Update to consistent PixieBrix branding

[corinnemayans]

The web site branding was updated, but the app branding was not. The inconsistency is a bad reflection on the PixieBrix brand and can erode trust.

We are using at least three different favicons today:

The web site and app are different:

Also, see example where logo background isn't transparent and looks bad:

For this issue, identify the places where there are inconsistencies and settle on one solution aligned with newest branding.