Polymorpshism for table cells objects #276

Currently table components Table and RosterForLoop use a dirty BodyCell object.

The reason ComponentType is not used instead is probably due to the fact that a table cell could be a simple static label, and LabelType has nothing to share with ComponentType.

Yet, Lunatic now uses a Text component, and it is recommended to use this one instead of a LabelType object in tables.

Then, it is now appropriate to refactor and remove the BodyCell object, to replace it by ComponentType.