Load power from xml (by a custom prorperty named "Power").
level1 => only sneeze
level2 => sneeze + fever
Fixes #60 :
* the dead must be set just once, overwise the level will try forever to load and reload, and reload and... etc
* Caution : the level reload so quickly that the death animation can't occur, and a timer won't fix this
Merge branch 'develop' of github.com:Symptogen/Symptogen into menus
Correction of bug related to the death of the player and the levels loading