Let units show their hp

Units now render their HP below them. The HP number is their procentual health divided by 10 rounded up. E.g 95% would be 10, 4% would be 1.
This way a unit will not display 0 Health which would imply that unit is dead.

(Optional) Hide HP until units HP fall below the 10 HP threshhold for less clutter.

changed milestone to %Implementation der UI und Game-Struktur

added Needs Review label

assigned to @frederik-alexander.keens

mentioned in commit 8796f9b4

merged