Add an option to use a command line interface in addition to the GUI

[airsquared]

A CLI would be useful for users to script as well as on devices like the Raspberry Pi. Picocli seems like a good library for this.

The CLI should be able to:

• Save blobs supplying all information as arguments
• Add/remove saved devices
• Export/import saved devices with XML
• Set up the background auto-save feature

Maybe:

• Interactively read information from connected devices too?