Add per-player killfeed modal

[TheLazySquid]

I noticed there was an unused endpoint in the backend for the killfeed and figured that it could be useful to see the history of a player's kills in order to make a verdict (for example to see whether a sniper has hit any bodyshots). I did my best to recreate the killfeed entries as faithfully as I could, but all the ids for kills were gathered in one long, boring afternoon and there may be mistakes here and there. (If an icon is missing it will fall back to the default skull).

Each killfeed icon is a few kilobytes, with all 200ish totaling to around a megabyte.

[megascatterbomb]

Couple quirks:

• The killfeed doesn't reset when switching maps/servers. Is this something we'd want to occur?
• The killfeed uses the player's team at the time of opening the modal to determine the team coloring for all kill events. I'd consider adding a team property to each killfeed entry so that discrepancies don't occur, though this may require further development on the backend to do cleanly.

[TheLazySquid]

Fixing either of those cleanly would probably require some work on the backend, unless there's some stuff I don't know about. It's also worth noting that the system of short polling the entire killfeed every second is really innefficient- after a few hours of play the killfeed will need to transfer a few hundred kilobytes per second.

With that said, I know next to no Rust, so I unfortunately won't be able to do much of anything.