display: Add UI to change nightlight color temperature

This adds a scale to change the color temperature between 2700K up to
6500K. A mark is added to the default value and a second one for
aesthetics.

Closes #147
11 jobs for benzea/nightlight-temperature in 3 minutes and 51 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #128092
build

00:02:16

 
  Test
passed #128094
asan

00:01:34

passed #128093
test

00:00:47

 
  Manual
manual #128099
allowed to fail manual
armv8
manual #128095
allowed to fail manual
flatpak
manual #128098
allowed to fail manual
msan
manual #128100
allowed to fail manual
ppc64le
manual #128096
allowed to fail manual
tsan
manual #128097
allowed to fail manual
ubsan
 
  Review
manual #128101
allowed to fail manual
review
manual #128102
allowed to fail manual
stop_review