Improve limitations for Algorithm Timer Interactive

[Alasdair Smith]

These hard limits for the Algorithm Timer interactive are far too restrictive when the complexity isn't at the top end (i.e. O(n!)), and as a result you can't even use it to do the exercises in the content. It would be far more sensible to remove/loosen these limits on lower complexities (perhaps O(n^3) and below), and warning users if they attempt to do it at higher complexities.