sensor: make non-restartable once data is received

The old criterion was if the start button had been clicked. However, sometimes, due to a misconfiguration, it's possible to click the start button but not get data. This makes it possible to fiddle with the configuration and click start again, without clicking reset.

IS [#54785632]
sensor: make isSensorConnected() test more robust

IS [#55588140]
IS [#55584106]
sensor: check for connected sensor before start()

IS [#55584106]
don't initializeSensor it's not connected!

IS [#54785632]
Don't disable stop just because model unstartable

IS [#54785632]