Finished first draft of the object file

First draft object_battleship.py file (without the tests, that need to be done in test_object_battleship.py). Contains a new class, Ship, used for ship placement. Replaced returns of True and False values by raises (cleaner and easier to implement in the project). Corrected some bugs caused by this modification, and corrected typing. This will allow the project to trully start, now that the main classes and methods are clearly defined (and working).

It is important to quickly create test functions for all the implemented methods. A 100% coverage must be achieved before going deeper into the project.