Move EDU program queue to FRAM

[PatrickKa]

Description

I am not sure how exactly to do that. Should the queue always be read from the FRAM or do we cache it in RAM? We also need to decide on the maximum size.

[PatrickKa]

Blocked by #185 and #192

[PatrickKa]

As explained in #294, we need a fallback mechanism in case the FRAM does not work. This means that the queue needs to be cached in RAM (maybe with a smaller size, though). If the FRAM works, queue entries are read from and written to it. Queue entries are also always written to the cache, but only when the FRAM doesn't work are they also read from the cache.

[PatrickKa]

Note that the queue index should also be stored on the FRAM as one of the persistent variables.