Polymorpshism for table cells objects

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`.