Update requirements.txt
Merge pull request #38 from oussemos/master

Adding 'requests' to requirements.txt
Update slides.py : Checking sqlalchemy Integrity
Merge pull request #40 from oussemos/master

Update slides.py : Checking sqlalchemy Integrity
Fixing #28 : le retour de addcategory corrige + test dexistance categorie + customisation du message de retour apres ajout