Monster loot off-switch

Adds a global off-switch cvar g_monsters_drop for monsters' loot drops.

Same off-switch for loot drops like Medium Health pickup and weapon drops like Vortex.

qcsrc/common/monsters/sv_monsters.qc

@@ -977,7 +977,7 @@ void Monster_Dead(entity this, entity attacker, float gibbed)
 	Monster mon = this.monsterdef;
 	mon.mr_death(mon, this);
 
-	if(this.candrop && this.weapon)
+	if(this.candrop && this.weapon && autocvar_g_monsters_drop)
 	{
 		.entity weaponentity = weaponentities[0]; // TODO: unhardcode
 		W_ThrowNewWeapon(this, this.weapon, 0, this.origin, randomvec() * 150 + '0 0 325', weaponentity);