add rasch functionality to form generation

app/lib/irt/item_response_function.py

@@ -1,4 +1,5 @@
 from lib.irt.models.three_parameter_logistic import ThreeParameterLogistic
+from lib.irt.models.rasch import Rasch
 from lib.errors.item_generation_error import ItemGenerationError
 
 
@@ -10,5 +11,7 @@ class ItemResponseFunction():
     def calculate(self, **kwargs):
         if self.model_data.model == '3PL':
             return ThreeParameterLogistic(self.model_data, kwargs).result()
+        elif self.model_data.model == 'RASCH':
+            return Rasch(self.model_data, kwargs).result()
         else:
             raise ItemGenerationError("irt model not supported or provided")