added class subject and grade

subject.py

@@ -0,0 +1,22 @@
+from datetime import datetime as str_date
+
+
+class Subject:
+    def __init__(self, name, main_subject, oral_exam):
+        self.name = name
+        self.grades = {}
+        self.main_subject = main_subject
+        self.oral_exam = oral_exam
+
+    def add_grade_category(self, name, rating):
+        self.grades[name] = ([], rating)
+
+    def add_grade(self, category, grade):
+        self.grades[category][0].append(grade)
+
+
+class Grade:
+    def __init__(self, grade, name, date=str(str_date.now())):
+        self.grade = grade
+        self.name = name
+        self.date = date