Add custom favicon if needed

[pourmand1376]

Hi, As I needed to customize my favicon and apply an icon, I thought this might be helpful for others as well. So why not create a pull request? #386

Here's how I think It should work. If the client sets use_custom_favicon to true, then he can provide a path instead of emoji in the icon. Otherwise, It works with emoji. So backward compatibility wouldn't be an issue.