Come out a non-hacky way for students to download input files

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As I can recall, when a user clicks the download button in the assignment table in the assignment page, the user only gets the first file if there are multiple input files, which is not correct and we didn't have a chance to resolve it in time before we released the last assignment. The goal of this issue is to make the download logic correct.

[PARanOiA1120]

Changes: For each row in the task table in the assignment page, there is a download button for input files, and this button will generate a zip file on-the-fly to allow students to download all input files in one click.

Have tested the following scenarios:

• Is able to fetch the correct zip file with the right content for each task
• Has done permission check so that
  • users who didn't enroll the course do not have permission to download any input files even though they know the download url
  • users with only view_assignment permission cannot download input files for tasks with Feedback or Hidden mode.