1.add joinUrl showing for developing purpose
2.fix related test
1. test whole join link shown in adminHomePage status
2. add comments for hidden instructor join link inside instructorCourseEditPageUitest and the asp file
Merge remote-tracking branch 'origin/master' into 74582646

Conflicts:
	src/test/java/teammates/test/cases/ui/browsertests/InstructorCourseEditPageUiTest.java
	src/test/resources/pages/instructorCourseEdit.html
fix instrcutorCourseEditPageUiTest
1. extract new instructor account joinUrl getting logic into a deprecated method
Merge branch 'master' into 74582646
[Fixes #74582646] show join link for admin and instructor adding for testing purpose