feat(DeviceFinder): add ability to get hand of controller

It's now possible to determine which hand the controller is for by
calling a new method `DeviceFinder.GetControllerHand(controllerObject);`
which can be useful for determining which controller is interacting
with an object. It can be used for example like so in the `StartUsing`
method of an interactable object:

`DeviceFinder.GetControllerHand(usingObject);`

This will determine which controller is being used to `Use` the obejct.

Author: thestonefox

Assets/SteamVR_Unity_Toolkit/Scripts/Helper/DeviceFinder.cs

@@ -49,6 +49,23 @@ public static ControllerHand GetControllerHandType(string hand)
             }
         }
 
+        public static ControllerHand GetControllerHand(GameObject controller)
+        {
+            var controllerManager = GameObject.FindObjectOfType<SteamVR_ControllerManager>();
+
+            if (controllerManager && controller == controllerManager.left)
+            {
+                return ControllerHand.Left;
+            }
+
+            if (controllerManager && controller == controllerManager.right)
+            {
+                return ControllerHand.Right;
+            }
+
+            return ControllerHand.None;
+        }
+
         public static bool IsControllerOfHand(GameObject checkController, ControllerHand hand)
         {
             var controllerManager = GameObject.FindObjectOfType<SteamVR_ControllerManager>();