Rework on-boarding

[boxdot]

The on-boarding of new users is not smooth enough. Some problems:

1. Config file needs to be created manually.
2. Config file contains the phone number even though it is only needed when linking the client for the first time #360.
3. Settings passphrase in the config file is confusing and is a security risk.

Bunch of ideas how we can improve it:

• On the first run (when there is no data yet), have a CLI wizard asking for the phone number, whether the db should be encrypted and and for the passphrase, and whether the passphrase should be stored in keychain/libsecret/somewhere else if possible. This wizard could be also a CLI form, but I think this is not needed since onboarding is done only once.
• Provide a user flow to decrypt/encrypt the data again. Again via CLI wizard?
• Add phone number CLI parameter. This removes the step in all wizards of providing the phone number.
• During on-boarding show the paths to the configuration/data.

[jarjk]

for the cli wizardry, I know a pretty neat library: dialoguer. it's quite lightweight, very stable and UX is awesome adoptation should be considered

[boxdot]

Just for the record: phone number is not required at all to run the app.

Onboarding is implemented in #391 (starts when there is no config found). Encryption is mandatory now #389.