Allow time-based triggered windows to be synchronized

[cjnolet]

Currently, all windows are independent with regards to time. Storm manages a ticking so that seconds can be incremented at the window level but, for instance, I an aggregator window should trigger every 50 seconds, the windows will start counting those 50 seconds based on when the window opened instead of a global 50 second interval set by the bolt.

There are cases where you'd want both, but specifically it would be nice to be able to lock the aggregators to the bolt's counter so that they all trigger at the same time.