syllabusTracker: fix issue that illegal characters in course name will cause generated JSON file to corrupt.

1. Use json_encode in `list1-initialCourses.php`, `list2-checkEnrollments.php` and `list3-gatherDetails.php` to properly encode JSON strings;
2. Add .gitignore file to exclude generated JSON file
Amend last commit
Merge pull request #1 from daiweilu/master

syllabusTracker: fix issue that illegal characters in course name will corrupt JSON files