Allow using connection file with password-protected keyring

This would be nice to mimic ssh keys and allow password-protecting the key and never have it on screen or terminal history.

mentioned in issue #15

assigned to @HugoTrentesaux

Example of commands:

gcli key generate
gcli key list
gcli key import
gcli key remove xxx

I plan to use sc_keystore to mimic duniter, but there might be better options.

mentioned in merge request !22 (merged)

closed with merge request !22 (merged)