Logarithmic scale for bar charts

[philosoralphter]

As discussed in #1790. Worked great for my line graphs but a couple bar graphs need it too.

I know a bar graph is usually used to visually compare sizes of each bar, but I am using it also to see breakdowns in a chart with split-bars. I don't need to compare the sizes of the entire bar as much as to see the top ten bars and the breakdown of each. Works great unless the top 1-3 bars are more than twice as tall as the rest of the pack.

[drorata]

+1

[harpreet-sawhney]

+1

[petemounce]

+1

[drewwoods]

+1

[ronsun669]

+1

[thomasneirynck]

duplicates #3437.

[thomasneirynck]

closed with #7939.

Only enabled for non-stacked bar charts.