Port code from hotspot test app to Briar

The MainViewModel and the WebServer from the hotspot test app need to be ported to Briar.

Subtask of #1081 (closed)

changed milestone to %Install via Bluetooth or Wi-Fi

added Sponsor 6 T: task labels

changed the description

mentioned in merge request !1461 (merged)

added S: in code review label

assigned to @grote

closed

removed S: in code review label

added R: fixed label

changed due date to July 31, 2021