Interpolate delta when a reading is missing

[bjornoleh]

In Nightscout, delta values are interpolated to 5 min interval values when a single (?) SGV is missing. This is giving more realistic delta values. It would be nice to have this incorporated in FAX as well

Nightscout:

---

---

FAX (ignore the UI mods)

I believe the NS code for this is here:
https://github.com/nightscout/cgm-remote-monitor/blob/46418c7ff275ae80de457209c1686811e033b5dd/lib/plugins/bgnow.js#L164