Added HTTP error code 400 when a BusinessException occurs

src/app.py

@@ -8,7 +8,7 @@ from flask import Flask, render_template
 import data.document
 
 def handle_exceptions(e):
-	return render_template("error.html", message = str(e))
+	return render_template("error.html", message = str(e)), 400
 
 def create_app():
 	app = Flask(__name__)