#182 Refactor the plugin-handler

[Gert Wollny]

The plug-in handler should be separated into two classes, one that takes care of collecting the actual plug-ins and one that takes care of handling the classes implementing the functionality. The idea is that one can implement a handler for a class hierarchy that doesn't load from external files but can be initialized like the current plug-ins.

[Gert Wollny]

This will be implemented in the branch translateparam.