Incorrect names of spin channels in PDOS

[giovannipizzi]

A name such as "CoS up" for an s angular channel, spin up, for Co, is not correct.

I would write this as :

Co (s↑)

(s in italics lower-case, use unicode for spin direction arrow, with some separation between atom and orbital, e.g. in brackets, ... - the only thing that I think can be different is that we can write s without italics).

This might be due to a bad original choice in AiiDA.
Since this might not be changed at this stage in AiIDA, I suggest two things:

• allow for an optional input in the __init__, e.g. pdos_names, with e.g. the following format {'CoS up': 'Co (s↑)', ...} to allow to change the label
• have a list of all possible strings generated by AiiDA, and write below (in this issue, so we can discuss) a table/dictionary of how we want to render (check the AiiDA code to see all options currently implemented, probably here). E.g. {'SP2': 'sp²', 'SP3': 'sp³', ...}'; this could be the default value of the dictionary. This might be probably enough to have nice labels for AiiDA-generated PDOS; if not, we might need to discuss if the python that calls the init` should generate a specific dictionary.

Pinging @mbercx and @unkcpz to both help @dou-du to check the API interface for the __init__, and check the final graphical result for the PDOS legend labels.