Changed all references of HP to Health

Changed all references of HP to Health
Moved the Use function from PlayerGO into ItemGO for different polymorphic uses of the different types of items. So far, they can only be used on players, but this opens up the possibility of using items on other items since Use() takes a shared_ptr<GameObject>

git-svn-id: https://svn.code.sf.net/p/gameservirc/code/trunk@524 bc333340-6410-0410-a689-9d09f3c113fa