Add an option to turn off beans check in SpringBeanLocator

In wicket 1.2.3, SpringBeanLocator.lookupSpringBean() force check all injected bean:

if (beans.size() == 0)
throw new IllegalStateException("bean of type [" + clazz.getName()
+ "] not found");

This check is good for production. But in test environment, it would be better that
we can turn off this check somewhere since test case does not always
prepare non-tested bean.