Print info from LHEF, if available

[kjvbrt]

BEGINRELEASENOTES

• Print x-sec error for Pythia process
• Print info from LHEF file, if used
• Print info from MadGraph LHEF file, if used

ENDRELEASENOTES

[tmadlener]

Unfortunately CI, doesn't really show the new output, but I trust it does the right thing? Then I would merge this.

[kjvbrt]

So the output looks something like this:

------------------------------------------------------------------------
                                                                                                           
Pythia8 Cross-section (f fbar -> H0 Z0 (SM)): 0.203 +/- 0.002 pb                                        
                                                                                                           
------------------------------------------------------------------------

And if the events come from the MG LHE file something like this:

------------------------------------------------------------------------                                   
                                                                                                           
Pythia8 Cross-section (Les Houches User Process(es)): 0.000 +/- 0.000 pb                                   
                                                                                                           
Input LHEF Cross-section:                                                                                  
 - sum: 0.000                                                                                              
                                                                                                           
Information from LHEF file:                                                                                
#  Number of Events        :       1000                                                                    
#  Integrated weight (pb)  :       6.4041e-09                                                              
                                                                                                           
------------------------------------------------------------------------