add GraphClustering to resolution scripts

Since Graph Clustering is the main calorimeter reconstruction algorithm in HLT2, i have updated the two resolution scripts: standalone_hlt2_calo_resolution_gamma and standalone_hlt2_calo_resolution_pi0 to run the Graph Clustering algorithm and also a default version of the Cellular Automata algorithm, just to keep a comparison.

If there is any other version of the Cellular Automata or Graph Clustering algorithm that is considered to be needed for comparison it can be added without problem.

This MR is ready for testing.