Clean up FeedbackQuestionSubmissionEditSaveAction #1861

Issue #1861
FeedbackQuestionSubmissionEditSaveAction
- branches not covered

+ Remove redundant conditional (Will never be true since exception is thrown above.)
+ Add test case empty recipient email
+ Add test case empty answer string
+ Add test case unsupported quesion type
+ Add test case Add response that already exists. (covers some branches in FeedbackResponsesLogic)
+ Add TODO test case for response question type not matching question's question type (related to #1862 )