Do batched retrieval of sensor entries.

[panmari]

This might help with more reliably fetch all data. When requestion 5k entries, occasionally some are dropped (usually the most recent ones). Jointly this enables a bunch of other optimizations:

1. Only retrieve new entries since last fetch, integrate entries with cached history.
2. Show partial history during retrieval.

[panmari]

1 Is now resolved

If retrievals are common, there's not much benefit for 2 as they're really quick.

[panmari]

2 could also be implemented using one retrieval, but streaming the results instead. That would allow updating the screen (and/or the cache) periodically.