feat(Interaction): add RequireComponents to grab and touch

Since InteractGrab and InteractTouch don't work unless certain
components are a part of the controller, the RequireComponent
attributes will make sure those components are there or automatically
add them. They also keep required components from being removed in
the Unity editor.

Author: bjennings76

Assets/SteamVR_Unity_Toolkit/Scripts/VRTK_InteractGrab.cs

@@ -16,6 +16,7 @@ namespace VRTK
     using UnityEngine;
     using System.Collections;
 
+    [RequireComponent(typeof(VRTK_InteractTouch)), RequireComponent(typeof(VRTK_ControllerEvents))]
     public class VRTK_InteractGrab : MonoBehaviour
     {
         public Rigidbody controllerAttachPoint = null;

Assets/SteamVR_Unity_Toolkit/Scripts/VRTK_InteractTouch.cs

@@ -18,6 +18,7 @@ public struct ObjectInteractEventArgs
 
     public delegate void ObjectInteractEventHandler(object sender, ObjectInteractEventArgs e);
 
+    [RequireComponent(typeof(VRTK_ControllerActions))]
     public class VRTK_InteractTouch : MonoBehaviour
     {