benchmark scripts: Extract partial backtransformation metadata

[albestro]

Changelog:

• extract (from_ev, to_ev) information (back-compatible, if not parsed set to (0, matrix_rows))
• calc_metrics for backtransformation algorithms now group also over from_ev and to_ev
• fix parsing (make patterns given to with_pattern non capturing): it was not causing any major problem apparently, but at least the number of threads was parsed incorrectly
• add a suffix with spectrum information to make plot filenames distinct to avoid overwriting
• add "tag" features used for analysis (mainly it indicates the cluster type) and try to merge it with the "label" feature (not fully tested)