Add ability to download seed phrase

[laremas]

related to this #363.

User will be able to download/upload the seed phrase. the buttons will be placed below the seed-phrase area (img below). in the creation flow and in the restore flow

Here is the component and here are the screens in the wallet file.

[deuch13]

@laremas The ability to download the seed phrase file will be given only to users that have set a password when creating/restoring the wallet.

[laremas]

let's keep this for a later discussion, I am not completely sure about how to implement it or if it is really needed at this point in time.

[Fulviuus]

We will check other wallets to see how they implement this feature, and then decide if we are going to move this to the backlog.

[nortonandreev]

I have checked a Wallet from another provider. Seems like they provide an option for the user to retrieve/backup the mnemonic from the Settings anytime after the wallet has been created.

[nortonandreev]

This is another popular Wallet – seems it also provides the option to backup/preview the seed phrase from the Settings, once the user has logged in.

cc: @Fulviuus @laremas

[laremas]

In case we add it, I would put download in the settings options as well, too.