Duplicate code in helpers.ts and course-helpers.ts

[MinhxNguyen7]

In #750, we found that there are two WebSOC caches. It turns out that a large part of course-helpers.ts is duplicated in helpers.ts. I vaguely remember extracting part of helpers into course-helpers, but I probably forgot to delete the old stuff.

As an aside, IMO, helpers.ts should be split up into multiple namespaces, whether that be different files, classes, or both.