Ask users to enable device encryption and a screen lock mechanism during setup

[cketti]

Our recommendation has always been to use Android's device encryption and a secure screen lock mechanism to protect the data stored by the app. However, this was never communicated inside the app.

When first setting up the app, we could check if device encryption is enabled and a screen lock is configured. If not, we should ask the user to do so in order to keep the data stored by the app protected in case the device is lost or stolen.