Persistence Plausible Deniability on Boot

Issue: When user creates persistent volume the presence of it is visible on boot, because the greeter asks for persistent volume password. Any person besides the owner can clearly see the presence of persistent volume by booting usb. Therefore, this poses a significant security issue.

Solution: Instead of prompting user to enter persistent volume password, user is required to add it as an additional settings instead. The persistent storage may exist or it may not and, therefore, there is no way to prove it on boot. This provides an elegant solution to plausible deniability on boot that only requires user interface change.

Related issues

• Is duplicate of #5929

Original created by @anonymous on 16750 (Redmine)