Consolidated multiple pd.concat calls into one in
compute_all_multioutcomes building hpar df. Addresses pandas
FutureWarning in concating an empty df and slightly more performant.

…precation-warnings

…precation-warnings

`set_index` call maintained prior behavior of creating an index like
0,1,...,N,0,1,...,N. Now the index goes 0,1,...,2N. This index does not
get used so it is a harmless breaking change.