#16 Support default arguments for directly instantiating actions

[Mirko Raner]

ActionRunner.getConstructorArgumentsFor(Class[]) already supports invocation of constructors that take an IWorkbenchWindow or IWorkbenchPage as argument (by simply using the current window or page). This mechanism should be made more general and should also be easily extensible. Additional types for which default values could be supplied:

- IViewPart (in conjunction with <action view="...">)
- Clipboard (new Clipboard for the workbench's display)
- Control (the workbench shell, maybe?)