message: Remove non-const PcaModel getter of MorphableModel
  It's no longer necessary, since the RNG is no longer part of PcaModel.
diff: @@ -82,20 +82,6 @@ public:
  return shape_model;
  };
  - /**
  - * Returns the PCA shape model of this Morphable Model.
  - *
  - * We need to have a non-const version because PcaModel::draw_sample(float)
  - * is non-const and modifies the object (the RNG). Maybe the RNG-stuff should
  - * be moved out of PcaModel into a free function that generates random coefficients.
  - *
  - * @return The shape model.
  - */
  - PcaModel& get_shape_model()
  - {
  - return shape_model;
  - };
  -
  /**
  * Returns the PCA colour (albedo) model of this Morphable Model.
  *
  @@ -106,20 +92,6 @@ public:
  return color_model;
  };
  - /**
  - * Returns the PCA colour (albedo) model of this Morphable Model.
  - *
  - * We need to have a non-const version because PcaModel::draw_sample(float)
  - * is non-const and modifies the object (the RNG). Maybe the RNG-stuff should
  - * be moved out of PcaModel into a free function that generates random coefficients.
  - *
  - * @return The colour model.
  - */
  - PcaModel& get_color_model()
  - {
  - return color_model;
  - };
  -
  /**
  * Returns the mean of the shape- and colour model as a Mesh.
  *
  