108536366: Implement register flow

Includes validation for gov.uk email address, mobile number with +44, password at least 10 char.
Form validation errors will be added to template in a later story.
User is created when form validates.

app/main/views/register.py

@@ -28,6 +28,6 @@ def process_register():
             users_dao.insert_user(user)
             return redirect('/two-factor')
         except Exception as e:
-            return jsonify(database_error='encountered database error'), 400
+            return jsonify(database_error=e.message), 400
     else:
         return jsonify(form.errors), 400