Define Window Function parameters

[AlasdairGray]

https://github.com/streamreasoning/RSP-QL/blob/master/Semantics.md#window-functions
A lot of parameters are used for window function parameters but are never introduced.

[AlasdairGray]

Also for time-based and count-based window functions

[AlasdairGray]

I still don't see why we have these window functions and then the substreams beneath. I think for the model we only need to define the substreams. The window operator generates these and is what has the input parameters.

[greenTara]

related to #32 , #33