[TASK] Raise compatibility to current state

This raises the compatibility to Flow 2.2.* and
Pheanstalk 3.0.*.

Besides, it does some code cleanup and uses DI and
Object Configuration for the Pheanstalk Library,
now since it's PSR-0 compatible; and uses the
configurable Event listeners as proposed in #2.
Merge pull request #6 from afoeder/master

[TASK] Raise compatibility to current state