Apply Clang cpp11-migrate tool to modify some trivial code

- Use "auto" keyword on some parts
- Use "override" in headers
- Use "nullptr" instead of "NULL" or "0"
(resources) Reorganize resources
(refactor) Move some classes into 2 new folders
(libraryModel) Fixed #2

When a QSqlQuery is initialized with a valid SQL request, it is executed
directly in the constructor. This was not the wanted behavior in this case.