Cell modifiers adapt the underlying model to an interface understood by cell
editors so that the cell editors can present the correct value to the user
and update the model with new values when a user has made modifications.
A editor action bar contributor defines the actions for one or more editors.
Within the workbench there may be more than one open editor of a particular
type.
A label provider maps an element of the viewer's model to an optional image
and optional text string used to display the element in the viewer's control.