Add trajectory to grenades, various refactoring

src/Dodge/Item/Weapon/Shell.hs

@@ -4,8 +4,8 @@ import Dodge.Data
 import Geometry.Vector
 
 import Control.Lens
-decTimMvVel :: Projectile -> World -> World
-decTimMvVel pj = projectiles . ix pjid %~
+decTimMvVel :: Prop -> World -> World
+decTimMvVel pj = props . ix pjid %~
     ( (pjTimer -~ 1) 
     . (pjPos   %~ (+.+ vel) )
     . (pjAcc   %~ rotateV rot )