show temperatures in Fahrenheit if the user has selected that in the normal gui

[Martin Bosma]

Reported on community:
https://community.victronenergy.com/questions/263432/farenheit-on-marine-mfd-app.html

Currently only Celsius is supported, even if the user has selected to show Fahrenheit.
It works in the gui-v1:

And gui-v2:

But not in the html5 app:

Related MQTT topic: N/<vrmid>/settings/0/Settings/System/Units/Temperature, supported values: "fahrenheit", "celsius".
Applies to: all temperature topics, i.e. battery, environmental, etc.

[Frank Waalkens]

Implemented in: 9de04e2