Override scaling on charts

[mutatrum]

For some values, it makes sense to set the scaling to a minimum resolution. Current behaviour blows every scale up until the graph fills almost the complete y-axis, but in most cases that just shows noise. F.e. hashrate graph is ok to be flat if the fluctuation is 0.01 Th/s.

This can be achieved by setting suggestedMin and suggestedMax on the min and max of the current dataset, but expanding those if they are too close together. So for example for hashrate, the difference between min and max should be around 10 Gh/s, so with 10 ticks each tick will be 1 Gh/s, which is fine. Closer up makes no sense.

Rinse and repeat for all metrics.