[Tails-ux] greeter UX mockups

Hi,

We recently made progress in the redesign of the greeter.

I updated the mockups with your last feedback, now at
https://tails.boum.org/blueprint/tails-greeter:_revamp_UI/

See also https://labs.riseup.net/code/issues/5464 for the associated
tickets. Don't hesitate to create yourself an account if you don't
have one and assign yourself tasks!

Cheers