Move all code related to state caching into one place

It is necessary to do some cleanup and add more junit tests to state saving code in MyFaces.

For PSS code, we just copied some parts of the original algorithm found on JspStateManagerImpl because just PSS was a very challenging task and the intention was prevent break existing code.

But now we have a stable code in this part, so it is the right moment to do some cleanup and then change the code to fit user's needs.