Add new CVar mp_free_armor

[AlexSwartz]

Resolves #560

• Implement the free_armor logic.
• Update game.cfg with mp_free_armor command
• Update readme with mp_free_armor command
• Register mp_free_armor cvar

// Give the player free armor on player spawn
// 0 - No armor (default behavior)
// 1 - Give Kevlar
// 2 - Give Kevlar and Helmet
//
// Default value: "0"
mp_free_armor 0

[etojuice]

Fix spaces.
Move the code that gives armor to OnSpawnEquip.

[etojuice]

If you want to replicate the feature from CS:GO, then you should know that in CS:GO players receive free armor regardless of being dead before spawning. In other words, give armor outside of GiveDefaultItems condition.