The postpone feature is missing as command line option

[ReneFroger]

Describe the bug
From what I understood, the Safeeyes has an postpone option. I would like to bind this to a key combination, but the safeeyes CLI doesn't have that ability to postpone the session for like 5 minutes. This should be added as well, I believe.

[deltragon]

When would you like to trigger this? In-between breaks, after a break has been announced, or after the break has started? (Or all three, I suppose.)
If it is either of the first two, it should probably be implemented together with #540, as it needs the same underlying logic.