fixes the stutter in animation when observer moves

There's a bug related to animations that have been playing for a long time, and have no "last frame" set... basically when this happens we don't properly roll over in the looping frame. The result is that when the scene's view angle is changed, the server re-sends the scene, and the client will roll the frame back do to rounding errors in the mod behavior and large floats.

The fix is the any animation loop that knows the number of frames in the animation (client playback and avatar animations) to set a "last frame hint" this last frame hit makes the roll-over work properly.

Another bug is that when an entity had a "loop" property of false, we wouldn't actually stop playing the animation at the final frame for exactly this same reason. This PR also fixes this bug.. but will have a side-effect on any scene where we were depending on this bug.

In particular, I believe that many of the animations in the "Castle" and "Apartment" are not set to loop. We will want to fix those animation settings when we merge this PR.