MIG-36-variant-group

[LaurentPetard]

Migration of the variant groups. The main difficulty was to regroup family and variant groups axes to be able to create the family variants.

[ahocquard]

You should avoid to use too much private functions that are replacing services. It breaks SRP too often and it's hard to understand/test.

You should split it in this PR, some things were hard to understand.

Two other concerns that could be fix in another PR:

• Prepared SQL request
• DestinationPim and SourcePim as services. Currently, you have to pass the parameter from function to function for no reason, as it's not dynamic (well, actually, just when you ask it to the user). What if you have a call stack of 10 functions, just because the last one uses DestinationPim? You have to pass it in the nine previous functions...

[LaurentPetard]

I will refactor DestinationPim and SourcePim as services in a side PR, because it changes the IVB migration too, and this PR is big enough.