Use last known time before power off or reboot

[Andersama]

This might be less useful for when power is lost, but when a reboot is attempted manually (this also applies for firmware updates) we could save and load on reboot the last known time, instead of falling back to a fixed date and time.

[mark9064]

This is already implemented but it doesn't work very well. With #2293 I have a more robust implementation so this should be solved along with steps persistence