Authenticate before seing data

[aberba]

Will be much secure if one has to authenticate with the Polkit agent to see the data of accounts. Just like one does to edit firewall, parental control or install an app in appcenter.

[cjfloss]

It's a good idea to restrict access to the information.

Right now the database would still be accessible by opening the database ($HOME/.local/share/com.github.cjfloss.envelope/database.db) with some SQLite program.

One alternative could be using SqlCipher to encrypt the database, allowing the user to define a password.