Refactor food item model and add barcode scanner page

Renamed FoodItems to FoodItem and Units to Unit in models.py, updated related imports and usage throughout the codebase. Added a barcode scanner test page using ZXing in the admin section. Improved food_items.html to display nutritional information in a table. Registered the admin blueprint in app.py and cleaned up blueprint registration in __init__.py. Updated seed.py to use the new FoodItem model.

seed.py

@@ -1,11 +1,22 @@
 from application import db, app
-from models import User, FoodItems
+from models import User, FoodItem
 
 with app.app_context():
     User.query.delete()
     db.session.add(User(username="admin", password="admin", is_admin=True))
     db.session.add(User(username="user", password="user", is_admin=False))
 
-    
-    
+    FoodItem.query.delete()
+    db.session.add(
+        FoodItem(
+            name="AH Matcha cookie",
+            energy=430,
+            fats=19,
+            carbs=59,
+            protein=5.5,
+            saturated_fats=10,
+            sugar=35,
+        )
+    )
+
     db.session.commit()