Make adding cellrenderers more discoverable in the treeview editor
Submitted by Rafael Villar Burke
Link to original bug (#595692)
Description
Adding a cellrenderer in the treeview editor now means using the context menu on a column, thus making it almost undiscoverable.
Perhaps this could be solved adding a third column to the hierarchy treeview, beyond the Label and Type columns, with a button for column elements which shows the context menu or, alternatively, adds a new (text) cellrenderer whose type can be changed in the type combo if needed.