Add a formatting option to convert temperature between Celsius and Fahrenheit

[carlos-sarmiento]

I live in the US but grew up on a metric system country and so my brain is used to thinking about Celsius. The other inhabitants of the house are very much used to thinking in Fahrenheit and find Celsius to be complete nonsense.

I want to be able to show temperature on both scales using the multiple entity row, but right now the only way to do this would be to create a bunch of template sensors with the conversion between the default in HA (in my case Celsius) to the other. Since this is some simple math, I was thinking it could be possible to use the formatting functionality on the card to do the math without having to create a bunch of sensors that effectively duplicate the data.

[carlos-sarmiento]

Saw that code was pretty easy to change so I jumped in and created PR #243

[benct]

Merged PR in version 4.5.0.