Support multi-signature unlock expression for Wallets

There is only two accounts with special unlock expression, that are ignored by py-g1-migrator.

These are multi-signature accounts.

Could someone help me implement support for them in the code?

Duniter V2 part only, how to express them in the output .json file?

Kimamila && Moul
SIG(38MEAZN68Pz1DTvT3tqgxx4yQP6snJCQhPqEFxbDk4aE) && SIG(GfKERHnJTYzKhKUma5h1uWhetbA8yHKymhVH2raf2aCP)
1002

Poka && Vit
SIG(Do99s6wQR2JLfhirPdpAERSjNbmjjECzGxHNJMiNKT3P) && SIG(7F6oyFQywURCACWZZGtG97Girh9EL1kg2WBwftEZxDoJ)
103