Arena quickfixes pack #1

In this patch I've fixed some of the most important problems of the Arena mode.

• Healthpoints, stamina and adrenaline meter are now persistent between rounds.
  
• If you have a usable item - you can use it once per 3 rounds (it resets after each 3rd round).
  
• Also after each 3rd round one of your healthbars is restored.
  
• Fixed drop of items - now only usable items drop on the Arena.
  
• fixed a long-standing problem with items' icons - they were wrong since launch.
  

And a couple more minor fixes!