Issue 1807
InstructorFeedbackQuestionAddAction
- It is currently possible to add questions with empty question text by modifying the js validator script.(instructorFeedback.js:64)

+ Added assumption to FeedbackAbstractQuestionDetails to assume questionText not empty.
+ Added test for empty questionText, expect assumption faliure.
+ Added test for non-existent enumerations of giver/recipient/question type, expect assumption faliure.
+ Added test for invalid questionNUmber
Merge branch 'master' of https://github.com/TEAMMATES/repo into Issue1807
Revert "Revert "marking for later reference""

This reverts commit 05810baf9701460fa6da46fd55cbd865ba656eea.
Revert "marking for later reference"

This reverts commit 15281f0b3fb0518be75885fa2ce8eb00eb5d4a6e.
Changed the parameters of feedback sessions from simply the typical values to increase coverage
InstructorFeedbackQuestionEditAction
- missing else case, line 59

+ Add else case, test and assumption fail when editType is invalid.
+ Add test and assumption for invalid question number.
+ Add comment on when some parameters are null.
Merge branch 'master' of http://github.com/TEAMMATES/repo
Remove catching and defining EntityDoesNotExistException since it is never thrown/not possible to be thrown by any method related.
Remove EntityDoesNotExistException since it is already caught by  function createFeedbackQuestion().
Changed an existing test case to expand coverage. Debugged a malfunctioning method
Added Assumption.assertNotEmpty/IsEmpty for String. Changed such assertions across TEAMMATES to use the functions.
undo some wrong changes
Added a modifyParamValue() function to make code in test/cases/ui/InstructorFeedbackQuestionAddActionTest.java clearer.
Added a TODO in FeedbackAbstractQuestionDetails to add a validate function.
Merge branch 'Issue1807' into Issue1810
changed and added a few test cases

used assertion instead of exception
added timezone tests
Change some tests to use modifyParamValue()
FeedbackQuestionsLogic: Remove TODO because test is already done in the first test in function.
Merge remote-tracking branch 'origin/master' into Issue1816
InstructorFeedbackEditPageUiTest
+ Added getter for maxNumScaleBox in InstructorFeedbackEditPage
+ Added test for numscale validation to check javascript.
+ Added TODO for numscale, currently, user is able to submit when min/max/step is empty and trigger an error page.
+ Added some TODOs for mcq/msq
Merge branch 'master' of https://github.com/TEAMMATES/repo into Issue1810
Refactor InstructorCourseDeleteAction