Improve first startup experience #572

Is your feature request related to a problem? Please describe.
Currently on first startup we just dump the user into the UI, with builtin no explanation on how to use it.
There is a guide on vorta.borgbase.com, but I would like for it to be an interactive setup and self-contained in Vorta.

Describe the solution you'd like
On first setup, guide the user through:

1. Restoring a backed up profile, and skip the rest if that happens (once Make Vorta profiles easy to backup and restore #462 gets resolved)
2. Adding a repository
3. Adding sources
4. Scheduling backups
5. Creating a backup of the new profile (once Make Vorta profiles easy to backup and restore #462 gets resolved)

And add a misc option to run this sequence every time a new profile is added

Describe alternatives you've considered
Improve the guide on vorta.borgbase.com with points 4 and 5.