Rework file reading and object extraction

* rename some functions to give a better idea what they are doing

* always compare all found objects

* remove code duplications

* make a user to specify the whole file path, fon't assume or add
  ".root" file extension

* same for files on the GRID: user has to give full GRID path. When path
  begins with ""alien", assume it is on the GRID and initialise

* remove pointers where not really needed

* use same extraction function for any ROOT input file, don't use
  specific ones for QC ROOT files and others

* wrap object extraction and plotting as much as possible

No changes have been made wrt the actual comparison and comparison
summary

* add very small python wrapper for convenience

Author: Benedikt Volkel