Now webgoatContext should effectively be a singleton, shared across
all WebSession instances. WebSession now initialises from WebgoatContext.
WebSession methods that refer to static "site wide" properties are deeted
and references to them updated to point to WebgoatContext
git-svn-id: http://webgoat.googlecode.com/svn/trunk@141 4033779f-a91e-0410-96ef-6bf7bf53c507