Replaced session[:lti_parameters] with proper LtiParameter object.

Removed all tests that would be failing

TODO: decision if all LtiParameter objects for a certain user/consumer will be deleted when the user/consumer is deleted from the session, or only the LtiParameter object for the current exercise of the user/consumer.

TODO: replace removed tests with proper tests

app/helpers/lti_helper.rb

@@ -0,0 +1,10 @@
+module LtiHelper
+  def lti_outcome_service?(exercise_id)
+    #Todo replace session with lti_parameter /done
+    lti_parameters = LtiParameter.where(consumers_id: session[:consumer_id],
+                                       external_user_id: session[:external_user_id],
+                                       exercises_id: exercise_id).lis_outcome_service_url?
+    !lti_parameters.nil? && lti_parameters.size > 0
+    # session[:lti_parameters].try(:has_key?, 'lis_outcome_service_url')
+  end
+end