#546 - import/export database: export default groupp too + handle default on import

...de/deadlocker8/budgetmaster/database/DatabaseService.java

...getmaster/database/model/converter/TemplateConverter.java

...er8/budgetmaster/database/model/v8/BackupDatabase_v8.java

...a/de/deadlocker8/budgetmaster/services/ImportService.java

.../java/de/deadlocker8/budgetmaster/templates/Template.java

...ocker8/budgetmaster/unit/database/DatabaseExportTest.java

...locker8/budgetmaster/unit/database/ImportServiceTest.java