Change keypairs file to encrypted format (DEWIF)

migrate to dup-crypto 0.11.1
remove all .seed access
Add option -f, --from-file to subcommands dunitrust keys modify network|member to add ability to import a DEWIF file.
Change keypairs file location to keypairs.dewif
At startup, if file keypairs.dewif not exist, don't create it alert user with a message like "no keypairs configuired, use temporary random network keypair". If file keypairs.dewif exist, Ask the user for the passphrase that will decrypt the file.

Edited Mar 01, 2020 by Éloïs

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