code: public FastAdapter<Item> withSavedInstanceState(@Nullable Bundle savedInstanceState, String prefix) {
          for (IAdapterExtension<Item> ext : mExtensions.values()) {
              ext.withSavedInstanceState(savedInstanceState, prefix);
          }
  
          return this;
      }
docs: re-selects all elements stored in the savedInstanceState
  IMPORTANT! Call this method only after all items where added to the adapters again. Otherwise it may select wrong items!
  
  @param savedInstanceState If the activity is being re-initialized after
  previously being shut down then this Bundle contains the data it most
  recently supplied in Note: Otherwise it is null.
  @param prefix             a prefix added to the savedInstance key so we can store multiple states
  @return this