Windowing doesn't allways propagate

[rafaqz]

Windowing (lazy views) don't always propagate right through from series -> stack -> array in all types.

This needs to be explicitly tested everywhere. It also needs to be clarified what happens to memory backed arrays - does window just switch to eager mode and use view recursively over its components?

It also needs to be clarified what happens when a series that holds actual stacks (instead of paths) has a window applied to it. If there is a window on the stack, how are they combined?