Feat: build tribe and student model

tests/model/test_student.py

@@ -0,0 +1,9 @@
+from backend.model.student import Student, Tribe
+
+
+def test_tribe_register_student():
+    tribe = Tribe("foo", "2nd")
+    student = Student("1", "Bob", tribe)
+
+    assert len(tribe.students) == 1
+    assert tribe.students[0] == student