Add +/- to Temperature Unit Converter

[Ahnassis]

Checklist

• [x] I made sure that there are no existing issues - open or closed - to which I could contribute my information.
• [x] I made sure that there are no existing discussions - open or closed - to which I could contribute my information.
• [x] I have read the FAQs inside the app (Menu -> About -> FAQs) and my problem isn't listed.
• [x] I have taken the time to fill in all the required details. I understand that the request will be dismissed otherwise.
• [x] This issue contains only one feature request.
• [x] I have read and understood the contribution guidelines.

Feature description

Turning numbers for temperature conversion negative.

Why do you want this feature?

So i don't have to use a different app for temperature conversions of negative numbers. As example -17.77⁰C to 0⁰F

Additional information

No response