Add internal module to facilitate animated IVAs

ie, when the sub-model that holds the IVA moves relative to the part.
It's just a simple parent-constraint that doesn't (yet?) support offset
position or rotation.

Source/InternalParentConstraint.cs

@@ -0,0 +1,36 @@
+using System;
+using UnityEngine;
+
+public class ELInternalParentConstraint : InternalModule
+{
+	[KSPField]
+	public string parentTransformName;
+
+	Transform parentTransform;
+
+	public override void OnAwake ()
+	{
+		if (part == null) {
+			return;
+		}
+		if (!String.IsNullOrEmpty (parentTransformName)) {
+			parentTransform = part.FindModelTransform (parentTransformName);
+		}
+		if (parentTransform == null) {
+			Debug.Log ($"[ELInternalParentConstraint] could not find {parentTransformName}");
+		}
+	}
+
+	void Update ()
+	{
+		if (parentTransform == null) {
+			return;
+		}
+		Vector3 pos = parentTransform.position;
+		Quaternion rot = parentTransform.rotation;
+
+		var xform = internalModel.transform;
+		xform.position = InternalSpace.WorldToInternal (pos);
+		xform.rotation = InternalSpace.WorldToInternal (rot) * Quaternion.Euler(90, 180, 0);
+	}
+}

Source/Makefile

@@ -26,6 +26,7 @@ EL_FILES := \
 	Hull/FaceSet.cs						\
 	Hull/RawMesh.cs						\
 	Hull/Triangle.cs					\
+	InternalParentConstraint.cs			\
 	Recipes/BuildCost.cs				\
 	Recipes/BuildResource.cs			\
 	Recipes/BuildResourceSet.cs			\