Screen changes from time deltas to timestamps after 15 minutes

[todd-herbert]

Changes the time deltas to timestamps in some situations, for E-Ink displays. extended to all displays

Conditions:

• Timezone must be set
• Timestamp must be at least 15 minutes in the past. Until this point, time delta is displayed

Impact:

• E-Ink UI is more static, fewer refreshes: avoids refreshing every minute to update time-deltas
• If configured correctly (if timezone set), much higher screen-timeout values are suitable (longer before screensaver appears)

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Allows users to disable the E-Ink screensaver, by setting screen timeout to zero.
If disabled, a cautionary message is printed to the on-screen log buffer at startup.

[caveman99]

Looking good to me. One point: is it useful to implement alternating behaviour for eInk only? i like the 15 minute cutoff for the time display, why not just enable it for all displays?

[todd-herbert]

Can certainly enable it everywhere if you think it's useful. It was just me trying to tread lightly!

[todd-herbert]

Just making minor adjustments