fix(Controls): rebuild grabbable slider object to work with snapping
fix(Controls): rebuild grabbable slider object to work with snapping

If a connected object is of a different scale to the child slider then
the snapping misbehaves. This is apparently a Unity bug where connected
objects that have a non uniform scale then cause connected joints to
not work correctly.

The solution is to have a dummy object that works as the interactable
object that has a 1,1,1 scale and then scale all children accordingly
to get it to look the same.

Innoactive/IA-unity-VR-toolkit-VRTK,mattboy64/SteamVR_Unity_Toolkit,Fulby/VRTK,gpvigano/SteamVR_Unity_Toolkit,gomez-addams/SteamVR_Unity_Toolkit,TMaloteaux/SteamVR_Unity_Toolkit,adamjweaver/VRTK,thestonefox/VRTK,red-horizon/VRTK,thestonefox/SteamVR_Unity_Toolkit,virror/VRTK,gpvigano/VRTK