An array of integers is now used to represent the SRP in three cases:
* In the import wallet flow, the UI uses it to pass the user-provided
SRP to the background (which converts the array to a buffer).
* In the create wallet flow, the UI uses it to retrieve the generated
SRP from the background.
* When persisting the wallet to state, the background uses it to
serialize the SRP.
Co-authored-by: Elliot Winkler <elliot.winkler@gmail.com>
