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'
the order of the mocks in the test method call is incorrect. It goes from the bottom up, so the first mock in the method call should be log_replacement