feat(startscreen): add exit/quit functionality

src/startscreen.py

@@ -7,6 +7,7 @@ class Startscreen:
         self.font_title = pygame.font.SysFont("Arial", 36)
         self.font_label = pygame.font.SysFont("Arial", 20)
 
+        # todo buttons must be initialized here
 
     def run(self):
         # set background color
@@ -17,5 +18,16 @@ class Startscreen:
         self.screen.blit(title, (10, 10))
         message = self.font_label.render("Welcome to FH - Study with purpose", True, (0, 255, 255))
 
+        # todo buttons must be drawn here
+        # todo check button events/click
 
-        return None
+        # check key down events - exit/quit
+        for event in pygame.event.get():
+            if event.type == pygame.QUIT:
+                return "quit"
+
+            if event.type == pygame.KEYDOWN:
+                if event.key == pygame.K_ESCAPE:
+                    return "quit"
+
+        return "startscreen"