CA, the legend is not displayed anymore in CA factorial map chart

Since 0.7.9 or 0.8.0 the legend is not displayed anymore in CA factorial map chart.

• define if we need this legend to be restored
• if yes
  • define the label texts: rows/cols or individuals/variables or some other texts
  • define if it must be displayed or hidden by default
• if not, disable the “Show legend” toolbar button for the CA chart as it’s done for the partition dimensions chart

(from redmine: issue id 2769, created on 2020/02/14 by Sebastien Jacquot)