speed up & refactor fitting/scoring.py

[PhilippKaniuth]

Speed up and possibly fuse both functions.

Suggestions:

• if score_type=='pearson':
  • use np.corrcoef to replace at least one for-loop (in case of scoring when multioutput & evaluating alphas: first change order of for-loops to then replace the then inner for-loop over targets)
• if score_type!='pearson':
  • use some sort of mapfunc
• use numba/etc for remaining for-loop