Persistence preset: Welcome Screen settings

Originally created by @segfault on #17136 (Redmine)

(sajolida is watching this)

Feature Branch: feature/17136-persist-greeter-settings;tps:feature/17136-persist-greeter-settings

Attachments

• Settings were loaded from persistent storage.png
• Start Tails button insensitive after typing a password but before unlocking.png
• Tails Greeter Settings preset in tails-persistence-setup.png
• Disable Admin Password.png

Subtasks

• #16998 (closed)

Related issues

• Related to #5501
• Related to #15641 (closed)
• Has duplicate #17698 (closed)
• Blocked by #17526 (closed)
• Blocked by #15122 (closed)

TODO

• Listbox in popover of loaded setting has the default value selected instead of the loaded value
• Popover broken after 1. adding Spoofing = enabled setting, 2. loading Spoofing = disabled setting from persistence