Minor default switching: loo2, remove unncessary feature & printing
Minor default switching: loo2, remove unncessary feature & printing

now the default is loo2;
unncessary feature computing phi from 0.25 * pi * sum of track-avg
psi is removed because it is not the right formulation;
printing to log file is reduced for longer running case.

lilulu/openmc,lilulu/openmc,lilulu/openmc