Uniform `weight` names in minimal initializers

[MartinuzziFrancesco]

This is a breaking change, but I think that the *weight names in the minimal initializers should be uniformed.

At the moment we have two distinct approaches co-living:

1. For simple inits like simple_cycle we just have weight as a kwarg
2. For inits with more complex structures like cycle_jumps the kwarg for the same structure is cycle_weight.

I think the second approach scales better and should be the goto, given that it could be possible to iterate over them using ie gridsearch in a much simpler way

[MartinuzziFrancesco]

This also applies to shift and fb_shift used to indicate the same shift in functions that use backward_connection!