Added Window to dictionary text/thrift formats

After this, shit is going to get real.
Window wouldn't be used to capture that part. It is only used to specify what data the entire query is over. Nested windows etc... would be part of the expression. 

As a general comment, we need to do a sweep and support time uniformly everywhere (chord/snapshot/windows etc...) at some point, but I don't think we should add bespoke for finer than day granlarity support on top of windows because it will end up being inconsistent and likely lead to problems when we want it to work the same everywhere.