Code cleanup (#1534)

* removed unused imports (no code change)

* Add missing @Override / @SupressWarnings (no code change)

* FIX: serialization warnings

* FIX: Access to static member

src/main/java/io/ebeaninternal/server/deploy/BaseCollectionHelp.java

@@ -42,6 +42,7 @@ abstract class BaseCollectionHelp<T> implements BeanCollectionHelp<T> {
     }
   }
 
+  @SuppressWarnings("rawtypes")
   @Override
   public Collection underlying(Object value) {
     if (value instanceof BeanCollection) {