Add Prop Hunt game mode

[garsipal]

Here's my vision for this game mode:

• repurpose the G key, currently used for dropping the CTF flag, to a versatile gameaction command. In the proposed Prop Hunt mode, this key will allow players to transform into props;
• props can either be randomly assigned from a pool of map models or selected by scrolling the mouse wheel, akin to choosing weapons;
• props will periodically emit distinct sounds to help hunters locate them;
• when players assume the form of props, they become stationary and are no longer affected by gravity. Returning to a "humanoid form" is necessary to regain movement capabilities;
• while in humanoid form, players can engage in combat with the hunter. However, damage dealt to the hunter will have a severe penalty, making it challenging to eliminate them. Hunters, on the other hand, can eliminate players/props with standard ease.
• points will be awarded to the hunter for capturing props and props will also earn points for surviving a round;