Support for MultiSig accounts

[DenisCarriere]

Currently there's no way to add the custom authorization for MultiSig enabled accounts using Scatter.

Scenario:
Using an account with a threshold of 1 and multiple active accounts all containing a weight of 1.

permissions: 
     owner     2:    1 user1@owner, 1 user2@owner, 1 user3@owner,
        active     1:    1 user1@active, 1 user2@active, 1 user3@active

I would like to "sign" a transaction using the authority of multisig@active, however I need to be logged in as user1@active.

When using eostoolkit.io and attempting to conduct a token transfer, it throws an error Missing required authority.