Control output directory and file naming of plotting functions

[mlincett]

Invoking the plotting function(s) creates outputs in the current working directory. There is no reco algorithm in the filename, so plots from different algos so filenames could clash.

I am thinking we could pass an output_dir (by default ./output) to the plotting routines and then have a minimal tree structure of the kind event_id / reco_algo.

[mlincett]

Will be solved by #22

[mlincett]

Output dir is configurable since #28 , still need to revise file naming.