v0.5.2 Release

New Feature: Flask port of student-client now can be configured through config.ini in the root directory.
Bug Fix: Fixed navigation failure of "管理学生名单。。。" card in the teacher-client's dashboard, and removed actual text placeholder in the student-client's login form.
Others: Gin is now working at Release Mode, which should improve server's performance, and server's ratelimit protection is removed.