Refactor `__str__()` in `DynModel` class
Refactor `__str__()` in `DynModel` class

Refacto `__str__()` in `DynModel` to return all the attributes of the
class. Since attributes can be dynamically added, the current version
uses `dir()` to return all the attributes and then convert them to
string.

galou/symoro,symoro/symoro,ELZo3/symoro,ELZo3/symoro,symoro/symoro,galou/symoro