Add ability to filter columns

[Forty-Bot]

Currently there is no way to filter columns client-side. Many of the pages on the site (e.g. /log or /player/logs) have fewer columns to prevent the content from becoming too wide. Similarly, many pages lack a variety of derived statistics (e.g. most do not include all of k, d, a, k/30, d/30, a/30, k/d, ka/d).

It is important to hint at this feature in the UI so users can tell when there are additional columns available.

Ideally this would be done client-side using a cookie or something like that. It could also be done server-side, but this would complicate rendering (which is already complex...).