Feature request: Store sensor data while offline for later upload

**Is your feature request related to a problem? Please describe.**

When a device is offline, its sensor values on the server are not updated, even after the device becomes online.
This causes stale data on the graphs:

**Describe the solution you'd like**

I am requesting two feature:
- One being the ability to store, then upload sensor data when the device becomes online.
- The other (if this is even possible) being that the graph should not show stale data. No information is better than wrong information.

**Describe alternatives you've considered, if any**

**Additional context**