Basic gameplay implementation

[xen-000]

Some basic gameplay mechanics that we need to get out of the way before doing anything else:

Infection System

• Move everyone to CTs on round start.
• Add a countdown with a minimum and maximum time for initial infection.
• Add human to zombie ratio configuration.
• Keep track of all initially infected zombies (AKA mother zombies).
• Infect anyone who spawns in after mother zombies are selected, this includes people switching teams, so probably best to hook player_spawn for that.

Gameplay

• Setup a rudimentary repeatkiller system that disables zombie respawning in order to end the round.
• Give proper kill credit to zombies who infect humans (maybe see how ze_collective does it)
• #38
• Figure out a way to keep killed humans in place while infecting them (like when a zombie right-click knifes them from behind).

Knockback

• Setup hitgroups for every player attachment.
• Setup knockback scaling depending on the weapon used and the human's class.

Classes

• Mother zombie class.
• Human class.
• Zombie class.

[Hichatu]

Basic gameplay is now implemented, knockback hitgroups and scaling is not too important for now.