Update: exploding barrel, rule changes, bugfixes

What's new:

• New placeable: exploding barrel. Acts as a platform (although it's affected by gravity), explodes when damaged by any projectile or another explosion.
• Explosions now destroy all projectiles (grenades will explode!).
• Shooting weapons is now allowed in safe zones and all projectiles pass through them as well, but still won't kill any players overlapping the safe zone.
• Placeable walls now fall apart instead of fading out.
• Saw blades won't take damage from arrows or pistol bullets.
• New small TNT "countdown" sound.
• Reduced weapon box spawn chance.
• Bugfix: TNT "countdown" sounds were not stopped if the TNT was prematurely destroyed (eg. by another explosion or a projectile).
• Bugfixes related to object shatter effects.