Rename as "Color Picker"

"Color Picker" was already the name in the UI.
This commit makes the appdata and README use this name.

Does not change the instances of `GColor3` within the code.

Closes #106
3 jobs for wip/christopherdavis/cosmetic-rename in 1 minute and 15 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #487494
flatpak

00:00:33

 
  Deploy
passed #487495
review

00:00:21

passed #487496
manual
stop_review

00:00:21