melodic demo: temporarily hide from menu

still didn't get around to finish it right, it's in an awkward
in-between state and does not really build on the differences
to scalar yet.

with a tear in our eye we send it off to a nap, but like a
worm emerges from its cocoon to grow into a butterfly this old
companion too will see the light of menu again more beautiful
than ever before. sweet dreams, it won't be long.

python_payload/apps/demo_melodic/flow3r.toml

 [app]
 name = "melodic demo"
-category = "Music"
+category = "Hidden"
 
 [entry]
 class = "MelodicApp"