Fix some generics warnings

I was going to push this directly to master, but stumbled upon some issues with Tap IMHO:

Why is it a subclass of AbstractModuleFixture? (It's not a module, and as such does not have a label). Moreover, the `label()` method of Tap now shadows the one of the same name from the base class, which has a totally different meaning. Finally, tapping can now only be done through one single concept, the "label" (which is either explicit or implicit). So label from tap should be removed, moduleName() should be renamed to something like moduleToTap() and that class should not inherit from AbstractModuleFixture.