Major rework of DEATHMATCH mode

Gameplay:
- Completely redesigned spawn system
- Servers are distributed by difficulty level: HARD (22 slots), MEDIUM (20 slots) and EASY (18 slots)
- Reworked bots, their complexity depends from mode category
— Added knife damage

Mode menu:
— Redesigned main menu to open !s or !dm in chat
— Added customization page: kill effect settings, statistics display settings
- Added an optimization page: the ability to hide unnecessary game effects
- Redesigned the settings page: weapon and game mode settings
- PREMIUM players now have the opportunity to create their own unique color effect on kill using RGB