modules/world: better separation of init functions

gamecore/modules/world/actors/actor2D.lua

@@ -1,15 +1,26 @@
 local Actor2D = Object:extend()
 
 function Actor2D:new(world, type, x, y, w, h)
+  self.type   = type or ""
+
+  self:setManagers(world)
+  self:initPhysics(x, y, w, h)
+
+  self:initKeys()
+  self:register()
+end
+
+function Actor2D:setManagers(world)
   self.world  = world
+  self.scene  = world.scene
+  self.obj    = world.obj
+end
+
+function Actor2D:initPhysics(x, y, w, h)
   self.x      = x or 0
   self.y      = y or 0
   self.w      = w or 0
   self.h      = h or 0
-  self.type   = type or ""
-
-  self:initKeys()
-  self:register()
 end
 
 function Actor2D:initKeys()