Proposition : model number handling (#4308)

* Try something for discussions

* Better alternative

* Typo

* Improve

* Change delimiter

* Move delimiter to space

* * Refactoring of CategorizedStorageFormat::load() and CategorizedStorageFormat::save() to support unused model slots
* Fix all unsafe usages of QString::toStdString().c_str()

* Fixed radio data import [Horus] (broken in 0f90ff0b65)

(cherry picked from commit cc12601a01)

* Added Q_OBJECT to TreeModel and some cosmetics

(cherry picked from commit f40e64c2aa)

* Cleanup

companion/src/modelslist.cpp

@@ -473,7 +473,7 @@ void ModelsListWidget::duplicate()
     while (i<getCurrentFirmware()->getCapability(Models)) {
       if (radioData->models[i].isEmpty()) {
         radioData->models[i] = *model;
-        strcpy(radioData->models[i].filename, radioData->getNextModelFilename().toStdString().c_str());
+        strcpy(radioData->models[i].filename, qPrintable(radioData->getNextModelFilename()));
         ((MdiChild *)parent())->setModified();
         break;
       }