Add relative class number #3301

Job	Run time
Initial setup	2s
devmirror lint	2m 0s
devmirror abvar/fq bianchi_modular_forms number_fields	3m 55s
devmirror galois_groups siegel_modular_forms	9m 4s
devmirror elliptic_curves hecke_algebras tests	3m 11s
devmirror hilbert_modular_forms sato_tate_groups tests	2m 36s
devmirror api characters cluster_pictures ecnf local_fields	3m 39s
devmirror belyi higher_genus_w_automorphisms hypergm lattice maass_forms tests users	2m 33s
devmirror artin_representations genus2_curves	2m 37s
devmirror classical_modular_forms	10m 40s
devmirror lfunctions	5m 36s
devmirror groups/abstract	4m 40s
devmirror modular_curves	4m 17s
	54m 50s

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