This is 3 years later, with no reply. I am going to answer this question for the other ~750 people who landed on this page.
There is “The Manual - Theming”:
You can change the following parameters of the look and feel on your instance:
[…]
Custom header logo and favicon as alternative to auto-generation based on logo
As you can guess from the last part of this sentence, it may be enough to upload a logo, as the favicon will get auto-generated.
Happy coding.