Implementing first mockup of aggregate hydrator as of zendframework/zf2#3829
Reusing hydration events in the aggregate hydrator
Removing unused constants/imports
Unit tests for the aggregate hydrator
Unit tests for the hydrate event
Merge branch 'hotfix/4451'

Close #4451
Extract event unit tests
Adding tests for the hydration listener
Adding integration tests for the aggregate hydrator
Using `array_merge` instead of
Adding event identifiers for the aggregate hydrator
CS fixes and docblocks for the aggregate hydrator namespace
Adding suggested dependency to zendframework/zend-eventmanager
CS fix (EOF EOL)
Merge pull request #4448 from Ocramius/feature/aggregate-hydrator

[WIP] Aggregate hydrator
Merge branch 'feature/4448' into develop

Forward port #4448