Migrator now returns a lostAccount array that includes objects
these objects include keys of address and privateKey,
this allows the MetamaskController to restore the lost accounts
even without customizing the idStore or the KeyringController.
Also includes a patch that allows idStore to synchronously export private keys.
Now old vaults are recognized as an "Initialized" MetaMask instance.
Upon logging in, when fetching the initial password-derived key, if there is no new-style vault, but there is an old style vault, it is migrated to the new format before proceeding through the usual unlocking steps.
