Persistent Storage redesign

Redesign done as part of tails#15572 (closed).

Welcome Screen
Persistent Storage
- Creation
- Navigation
- Features
  - Data usage
- Deletion
- Locked
- Dialogs
Just-in-time help
Menus

Welcome Screen

First screen

The Welcome Screen is split into 2 screens to make it easier to handle the additional settings stored in the Persistent Storage.

When it's impossible to create a Persistent Storage (eg. ISO image), the Welcome Screen could still be displayed in a single screen and save users some extra clicks.
I also tried using a button instead of a switch. P2 didn't pay attention to the switch with a label aligned on the left and later commented than a button was more visible. P5 commented that the switch made it clear that it has 2 states, while a button is more ambiguous and could mean that it will lead you somewhere else in the interface.

That's why I settled on a switch with a label close to the switch.
The locale formats are not displayed in the first screen because we don't need them to be saved unencrypted on the USB stick and they are less important than language and keyboard layout.

I used:

The image of the backpack for discovery as it explains the concept better than a simple lock, as commented by P2.
The icon of a closed lock wherever possible to depict a locked Persistent Storage.
The icon of an open lock wherever possible to depict an unlocked Persistent Storage. P4 wasn't sure whether she could save file to her unlocked Persistent Storage when I used the icon of a closed lock for the Persistent folder in Files.

The open/closed lock help newcomers that are unfamiliar with such encryption to build their mental model of how the Persistent Storage worked and what was possible in which state, especially right after creation.

I always used a closed lock in the Applications menu because I didn't think that it would easy to change it depending on the state of the encryption.

Language

Second screen

The second screen displays all settings upfront.

When we redesigned the Welcome Screen in 2015, we thought that we would end up adding quite a lot more of such settings and made a design that could be easily extended. Five years later, we didn't add any and we're actually planning on removing some: Network Connection to begin with and ideally Unsafe Browser and MAC Address Anonymization, which depend on the network and shouldn't be immutable for the entire session.

Persistent Storage

Creation

Navigation

Now that we can turn features off and on without restarting, could we delete a Persistent Storage while unlocked?
Instead of having a Delete button in the title bar, another "GNOME way" would be to put the Delete and Change Passphrase buttons in the hamburger menu.

Hamburger menus have poor discoverability and 2 out of 3 test participants didn't find the Delete button when I put it there, though admittedly it might be even harder to discover on paper prototypes.

Change Passphrase being for now the only other such button, it doesn't hurt to put it at the bottom of the scroll and will be more discoverable than in an hamburger menu.

Features

The gear buttons opens relevant dialogs to change each of these settings. See the Dialogs section below.

I only added an info button to the Dotfiles feature because it was the most obviously in need of one. The settings from the Welcome Screen are better explained there. We could add a few more info buttons while avoiding overcrowding the screen.