Fixed recursive lookups in the hydrator manager

This should fix #19  and #25:

- Removed the HydratorManager
- Removed Hydrator invokables in module configuration
- Added the abstract factory directly to the HydratorsPluginManager

Note:
In existing generated API module configurations, the hydrator invokables MUST be deleted. Otherwise you will retrieve a ServiceManager error which tells you that the classes do not exist! (so this commit breaks BC)

I could not reproduce the state of #25, but normally this should fix it! Please check before merge :-)