Add CLI command or extra script for converting keys

[jfinkhaeuser]

During signup, it's possible to create unencrypted JSON files for the role account. Those unencrypted files cannot be easily imported into the UI (see https://github.com/Joystream/apps/issues/108).

The CLI could easily provide commands or extra scripts for:

• Adding/removing passwords to/from JSON files.
• Extracting the raw seed from a JSON file.

[jfinkhaeuser]

Try to accept seeds for the member account, and try to display the actor account seeds, too.