Added Plugin "Killstreak"

This little Plugin is currently included in the NS2Stats mod.

But as it works without NS2Stats maybe add it to Shine.

In generall it prints out Killstreaks in the Chat.

Also it has the option to play Quake Sounds but those sounds can be muted with sh_disablesounds by Client. Also SendSounds is false by default.

Documentation: https://github.com/BrightPaul/NS2Stats.com/wiki/Killstreak

The code should hopefully fit to Shine style ;) The sounds have to be in folder sound somehow.