Implementing and re-utilizing an abstract aggregate listener

as of zendframework/zf2#3874
Adding trait and tests for the aggregate listener detach logic
Reverting the naming from 'callbacks' to 'listeners' for callback handlers in aggregates
Merge pull request #3876 from Ocramius/feature/abstract-aggregate-listener

Implementing and re-utilizing an abstract aggregate listener
[#3876] CS fixes

- EOF ending
Merge branch 'feature/3876' into develop

Close #3876