Allow inversion of charts's scales for expenses

Currently, when generating a line chart (or line graph, whatever it's called in English), for expenses, the results are presented in the negative scale of the "amount" variable - on the bottom half of the chart.

It would be good to have the possibility to reverse the scale: presenting negative values in the upper half of the chart, and positive values in the lower half. It is generally more useful, in my experience, to see an increase in expenses as a line going up, through the "time" variable, than a line going down, as it currently is, with the negative values in the bottom half of the chart.

I hope I explained myself clearly: this should be easy to implement, I think, if the author or other users find it relevant. I'm not even sure if this has been reported before, because I didn't know exactly how to search this subject. Thank you.