Split lookahead days into lookahead trigger and lookahead window

[stheid]

The lookahead trigger selects whether a new email is triggered, but it might be cooler to send emails still as seldom as currently (with lookahead days) but make them more informative, adding also more future slots.

Its probably cool to highlight the lookahead trigger days, to make clear those are imporant, but also display also empty pickups that are further in the future.