Favicon on build page

[humitos]

On build page, it would be good to change the color of the favicon depending on the status of the build:

• yellow when it's triggered
• orange while it's building
• green when it succeeded
• red when it failed

[agjohnson]

This is a small feature I've wanted to add when I get to adding polish features. It might be mostly for us, as we tend to be the ones watching build pages progress the most frequently 😆

But either way, I think it's a nice UX and it shouldn't be hard to implement (I could be wrong here though).