Option to indicate the mean using a bar instead of plus sign

[GreenSeaSlug]

The 'Add sample means' function uses a '+' sign to indicate the mean. This is OK when showing a box plot (given the median is indicated by a bar) but looks weird when showing a dot plot (e.g. for small sample sizes). Would be great if the mean was indicated by a bar instead, or if there was an option to choose either a plus sign or a bar to indicate the mean.