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/radiodata.cpp

@@ -96,9 +96,8 @@ void RadioData::convert(Board::Type before, Board::Type after)
   for (unsigned i=0; i<models.size(); i++) {
     models[i].convert(before, after);
   }
-  
   if (categories.size() == 0) {
-    categories.push_back(CategoryData(QObject::tr("Models").toStdString().c_str()));
+    categories.push_back(CategoryData(qPrintable(QObject::tr("Models"))));
     for (unsigned i=0; i<models.size(); i++) {
       models[i].category = 0;
     }