ViewModel Cleanup (in hotspot test app)

Subtask of #1081 (closed)

changed milestone to %Install via Bluetooth or Wi-Fi

added Sponsor 6 T: task labels

assigned to @sebkur

cleanup ideas:

• Status enum instead of hardcoded status strings (let UI decide about actual messages displayed etc)
• Separate web server and WiFi hotspot managing code from view model, move into own classes to separate concerns
• let view model implement ActionListener and maybe also GroupInfoListener
• remove things we won't need
• make sure the intended flow of the UI is properly modeled by the view model
• prepare injectability
• loading
• error handling

added S: in progress label

added S: in code review label and removed S: in progress label

closed

removed S: in code review label

added R: fixed label

changed due date to July 31, 2021