Import/Export class names are really confusing

[opcoach]

The names for export management are confusing. We have :

• Export : the service to select the right IExport instance or the right IImport instance
• IExport : the interface to be implemented to export
• ExportXML : an implementation of IExport
• ExportCSV : another implementation of Export
• IImport : the interface to be implemented to import but actually never implemented...

These names would be more convenient :

• IExportService : the interface for the export service -> should provide minimal interface to export
• IImportService : the same for import
• ExportService (internal), our implementation to export by reading extension points
• ImportService (internal) the same for import
• IExporter : the interface to be implemented for an exporter
• ExporterXML : the XML implementation for XML (implements IExporter)
• ExporterCSV : the CVS implementation for CSV (implements Exporter)
• ImporterXML : the XML implementation for XML import
  ...

If we use the pure E4 injection context, we will provide both services in the context. If we still use E3 development, we will provide a singleton in services to get the default implementation. For instance : IExportService.getDefault() will return the internal implementation or better, the ExportService is declared in an OSGi component file. This will simplify also the tests if we want to provide other importer/exporter.