getListData
Gets a set of data from the memory cache.
    connection.getListData(set)
  
  Goes through each set add by updateListData. If
set is a subset, uses algebra to get the data for the requested set.
Parameters
- set 
{Set}:An object that represents the data to load.
 
Returns
 {Promise<ListData>}: 
A promise that resolves if set is a subset of
some data added by updateListData.  If it is not,
the promise is rejected.