message: Updated images types in fit-model-multi
  This makes it compile again.
diff: @@ -270,8 +270,8 @@ int main(int argc, char *argv[])
  Eigen::Matrix<float, 3, 4> affine_from_ortho =
  fitting::get_3x4_affine_camera_matrix(per_frame_rendering_params[i], images[i].cols, images[i].rows);
  // Have to fiddle around with converting between core::Image and cv::Mat
  - Mat isomap =
  - core::to_mat(render::extract_texture(per_frame_meshes[i], affine_from_ortho, core::from_mat(images[i])));
  + const core::Image4u isomap =
  + render::extract_texture(per_frame_meshes[i], affine_from_ortho, core::from_mat(images[i]));
  // Draw the loaded landmarks:
  Mat outimg = images[i].clone();
  @@ -305,12 +305,14 @@ int main(int argc, char *argv[])
  cv::imwrite(outputfile.string(), core::to_mat(frontal_rendering));
  outputfile.replace_extension("");
  + cv::Mat isomap_opencv = core::to_mat(isomap);
  +
  // And save the isomap:
  outputfile.replace_extension(".isomap.png");
  - cv::imwrite(outputfile.string(), isomap);
  + cv::imwrite(outputfile.string(), isomap_opencv);
  // Merge the isomaps:
  - merged_isomap = isomap_averaging.add_and_merge(isomap);
  + merged_isomap = isomap_averaging.add_and_merge(isomap_opencv);
  }
  // Save the merged isomap:
  @@ -326,9 +328,9 @@ int main(int argc, char *argv[])
  morphable_model.get_shape_model().draw_sample(pca_shape_coefficients),
  morphable_model.get_color_model().get_mean(), morphable_model.get_shape_model().get_triangle_list(),
  morphable_model.get_color_model().get_triangle_list(), morphable_model.get_texture_coordinates());
  - std::tie(frontal_rendering, std::ignore) =
  - render::render(neutral_expression, modelview_frontal, glm::ortho(-130.0f, 130.0f, -130.0f, 130.0f),
  - 512, 512, render::create_mipmapped_texture(merged_isomap), true, false, false);
  + std::tie(frontal_rendering, std::ignore) = render::render(
  + neutral_expression, modelview_frontal, glm::ortho(-130.0f, 130.0f, -130.0f, 130.0f), 512, 512,
  + render::create_mipmapped_texture(core::from_mat_with_alpha(merged_isomap)), true, false, false);
  outputfile.replace_extension(".frontal.png");
  cv::imwrite(outputfile.string(), core::to_mat(frontal_rendering));
  outputfile.replace_extension("");
  