feat: ordered concerning/reassuring feats by contribution size

[slebastard]

Marginal additions/modifications to explainability module:

• sorting expl_selection lists select_concerning and select_reassuring so that the lists are ordered by decreasing contribution size
• reversing the direction of radar variables
• grouping categoricals and continuous features of group retards_paiement into a single micro_variable retards_paiement, or equivalently, using the macro variable retards_paiement as the only micro variables for retards_paiement
• adding unit tests for functions generating expl_selection variable

[slebastard]

Please merge #70 before this PR.

70 affects the codebase in a broader way, and rebasing feat/explain_v2 on develop after merging feat/e2e_list_production will be easier.

[vviers]

@slebastard can you please rebase this branch and resolve conflicts before I can review and merge it ? :)

[slebastard]

@slebastard can you please rebase this branch and resolve conflicts before I can review and merge it ? :)

Rebase done, you should be good to go!