replace clusters_bins with capacity_bins

[MRossol]

Implementation of #47
Replace cluster_sc_bins with capacity_bins

• For each "resource"-"class" group create the given number of equal capacity bins, by default 3
• Fill bins with cumulative capacity after sorting by the given column(s), by default "trans_cap_cost"

Misc:

• config class updated
• reeds_cli updated
• example configs updated
• tests updated

[MRossol]

fixes #50

[grantbuster]

If you have time I would suggest doing a verification test by doing some mean/stdev on the classifier output equal capacity bins. This would basically be a sanity check on the outputs. Would serve to complement the baseline validation test. Not necessary if you're busy.