This is kind of a continuation of #1334.
In the discussion for that issue I briefly considered the point that a transposed BarSeries could more or less replace a ColumnSeries. The main differentiation between these two series seems to be the label placement. This however could be easily resolved by a similar approach as was introduced in #1334 for the HistogramSeries:

As a proof of concept, I modified BarSeries accordingly and tested in in transposed mode:

So this makes me wonder: Is there a compelling reason to keep the ColumnSeries as a separate class when we can get the same plot using a transposed BarSeries?

Immediate Benefits would be:

• Less code duplication
• Simpler API
• Derived Series would automatically also be transposable (e.g. ErrorColumnSeries)
• Easier switching between horizontal and vertical Bars

The main downside is that this would involve quite some breaking API changes. These are the main changes I can think of right now:

• Remove BarSeriesBase and BarSeriesBase<T>, move functionality to BarSeries
• Remove BarItemBase, move functionality to BarItem
• Remove ColumnSeries, ColumnItem
• Rename ErrorColumnSeries to ErrorBarSeries and make it inherit from BarSeries
• Fix BarSeries to work in transposed mode (as shown above)
• Remove ColumnSeries examples
• Add transposed versions of BarSeries examples

What do you think? Did I miss something? Is it worth it?