Balancing the game and arena mode

-Added loot to the newest boss: 

     *Death Sword 

     *Hp ore boost | hp -> +9 | max -> 3 | TOTAL -> +27hp

-Added arena mode:

     *Enemy hp -> +80%

     *Boss hp -> +35% * scale | Scales with weapon damage

Changes in multiplayer and singleplayer:

     *Changed a lot how the damage system works

     *Enemy hp boost in multiplayer changed | +80% -> +60% |

Stats:

-Max Hp changed | 123 -> 150 | because of hp ore

-Max damage | 4 -> 5 | because of death sword

-Hit speed of death sword is the same of magma blade