private boolean isInjectable(Class<?> aClass) {
    ConfigurationObject annotation = aClass.getAnnotation(ConfigurationObject.class);
    return annotation != null;
  }
Maintains a registry of global Spock extensions and their configuration objects,
which can be used to configure other extensions.

@author Peter Niederwieser
spock-core/src/main/java/org/spockframework/runtime/GlobalExtensionRegistry.java