Slashes in course names/course categories makes tracking work oddly in Matomo

[peterspicer-catalyst]

Since / is used as the separator for Matomo, if there's a course name or category with / in it, this won't be picked up or separately escaped.

I haven't tested this behaviour for Google Analytics, but for Matomo, I've fixed this by changing the might_encode function to not only encode ' with a backslash, but also encoding / as a - when it would otherwise turn up in course names etc., as the use case is historical convention of 2019/21.