Implement gamemode integrations

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Gamemode integrations would, as the name implies, integrate specific parts of a gamemode in the client UI.
Some mockups of how gamemodes would look like:

Babel

Show the name of the player who is holding the intel. The player's name would also match the color of their team.

Implementation

Using the IntelPickup packet.

Arena

Show the number of players who are still alive for each team.
Countdown should also be shown here when the round hasn't started, and then being replaced with the number of alive players instead when it starts.
Round ends would show the winning team only, or maybe making the other team be grayed out (and reset when the next round starts).

Implementation

Scraping the chat messages for countdown, using the regular player list for alive count.
Possibly using a protocol extension for countdown, if it gets decided.