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/storage/otx.cpp

@@ -93,7 +93,7 @@ bool OtxFormat::write(const RadioData & radioData)
 bool OtxFormat::loadFile(QByteArray & filedata, const QString & filename)
 {
   size_t size;
-  void * data = mz_zip_reader_extract_file_to_heap(&zip_archive, filename.toStdString().c_str(), &size, 0);
+  void * data = mz_zip_reader_extract_file_to_heap(&zip_archive, qPrintable(filename), &size, 0);
   if (!data) {
     return false;
   }