Set Default Allowed Lateness to Zero and Make Triggers Non-Purging

In preparation for upcoming changes in 1.2 we should set the default allowed lateness to zero and make all built-in triggers non-purging by default.

Currently, EventTimeTrigger and ProcessingTimeTrigger purge when they fire. This leads to unexpected behavior when a user sets some meaningful allowed lateness. The behavior will be that the window is purged when firing and the state will not actually be kept within the allowed lateness.

Changing the behavior to non-purging requires changing the default allowed lateness from Long.MAX_VALUE to 0. Otherwise we would have memory leaks.