[Tails-dev] Please review and merge feature/logo into stable

Sorry for the short delay, but here is the branch that integrates the
logo in the most critical places:

- SVG source for the logo in different forms
- website
- splash screen

Branch: feature/logo
Tickets:
- #7088: Integrate the new logo in the banner
- #7089: Replace titles font with Source Sans
- #7091: Credit the USB icon author
- #7093: Create a boot screen with the new logo
- #7094: Integrate the new boot screen in syslinux

On the 1.0 roadmap two things are left undone (I think):

- #7095: Integrate the new logo in Tails Installer
- #7096: Integrate the new logo in About Tails

But that's on alan's plate. I think he already got working prototypes,
so I'm adding him in Cc, let's see if he can make it on time.

--
sajolida