New unit - allow specifying number of significant figures rather than number of decimals

<!-- Please only use this template for submitting feature requests --> **Why is this needed**: In some graphs, depending on the filter I may be showing data with very different magnitudes (eg 123,456.000 or 0.00123456) In the standard options section, i typically display values as "short". unfortunately, while this works for large values, it does not work for values <=0.01, displaying only thousandths -> few sig figs. Same goes for "number, which is also difficult to read for values > 1e6. SI short works the best as it retains a consistent # of sig figs, but I would prefer to not have the scale suffix at the end **What would you like to be added**: An option to set the # of sig figs in standard options rather than setting decimals **Who is this feature for?** Users reading financial data frequently look at data which may vary over many orders of magnitude, so I would expect it is useful for them