#203: Update CoreConfiguration

- Updated CoreConfiguration to be able to get a BeanConverter from it.

src/main/java/io/beanmapper/config/CoreConfiguration.java

@@ -468,6 +468,6 @@ public BeanConverterStore getBeanConverterStore() {
 
     @Override
     public <S, T> BeanConverter getBeanConverter(Class<S> source, Class<T> target) {
-        return null;
+        return this.beanConverterStore.get(source, target);
     }
 }