Get rid of data in PSNodes

[mchalupa]

Do not store the data directly in PSNode, store them somewhere aside. It will be more clear than having them in the nodes. And it won't have any overhead, since instead of n pointer in the nodes we can have an array of n pointer (and we can use id's of nodes -- if we add them -- to have a constant-time access).

[mchalupa]

Now we have everything prepared (ids in nodes) for this change, so I'm marking this issue as a bug since now the data attribute is redundant and breaks thinks (cannot run multiple analyses at once this way)