Feature/sections sapna unittests

Fixed unit tests for create_section_form, get_enrollments_without_test_student , remove_section and created separate test files for these. Also added new test casesin these methods for the new utilities 'check_resource_link_id' and 'validate_course_id'
I think the @patch statements should be right on top of the method call. It may not be required, but I think it's sort of a standard practice. It's just a suggestion.