Update Package Lists on First Boot so Users can Easily Install Packages

Created by: NickDaly

Packages can't successfully be installed until the package list is updated. Currently, users must do this in Plinth manually, by running "Unattended Upgrades." This makes installing and activating your first service a two-step process, where you can't activate a service until the upgrade process is complete.

This may also be resolved by fixing #77 (closed).