Replace favicon.ico to unify our branding as a project.

Hi. I am trying to get the project to use a unified branding. One recognizable logo. To achieve this I would like all projects to use the same favicon.ico. The one from https://ubports.com/favicon.ico contains icons in multiple sizes, contains the Yumi head logo and also the "UBports" name, for those unfamiliar with Yumi. Please accept this PR. Kind regards, Jeroen Baten Operational Marketing Manager UBports Foundation.