fixed problem with cascade delete in orientdb-object.

the method getCascadeDeleteFields(String iClassName) is 
looking after entries of fields to delete by classname, in the mao
cascadeDeleteFields and ignores cases with superclasses.
Now the method looks after the registered class with the name iClassName
and returns the result of  getCascadeDeleteFields(Class<?> iClass) which
handles superclasses

Issue: #3172