Centralized Tick Counter, Fix Actor Dragging Bug

* The game's tick counter was moved from Doodle.ticks to shmem.Tick
  where it is more easily available from every corner of the code.
* Fix a bug in the Level Editor where dragging an already-existing actor
  from one part of your map to another, would cause it to lose all its
  data (especially its UUID), breaking links to other doodads. Now the
  existing Actor catches a ride on the drag object to be reinserted
  later.
* Animate the Link Line visualizers between actors. They now animate a
  blinking color between magenta and grey-ish.

interface.go

@@ -189,6 +189,7 @@ var (
 	Cyan       = RGBA(0, 255, 255, 255)
 	DarkCyan   = RGBA(0, 153, 153, 255)
 	Yellow     = RGBA(255, 255, 0, 255)
+	Orange     = RGBA(255, 153, 0, 255)
 	DarkYellow = RGBA(153, 153, 0, 255)
 	Magenta    = RGBA(255, 0, 255, 255)
 	Purple     = RGBA(153, 0, 153, 255)