Enable setting of mobility precision and add test

model/leo-circular-orbit-mobility-model.h

@@ -70,6 +70,16 @@ private:
    */
   Vector3D m_plane;
 
+  /**
+   * Current position
+   */
+  Vector3D m_position;
+
+  /**
+   * Time precision for positions
+   */
+  Time m_precision;
+
   /**
    * \return the current position.
    */
@@ -94,6 +104,15 @@ private:
    * Advances a satellite by a degrees on the orbital plane
    */
   Vector3D RotatePlane (double a, const Vector3D &x) const;
+
+  /**
+   * Calculate the position at time
+   *
+   * \param t time
+   */
+  Vector CalcPosition (Time t) const;
+
+  Vector Update ();
 };
 
 }