Combine all Chart datapoint values in hover-over.

The hover-over displays all of the values using the same timestamp, instead of just one value.
This is useful because you then get a overall data snapshot, and then can easily compare values to identify problems.
Example; energy data can be volatile, but by displaying all values at a timestamp its easy to do basic maths to identify discrepancies.

**Flexdash example**

**Grafana example**