import vxl.vgl.algo so vgl_rotation_3d can be loaded as a python type

it is necessary to import vxl.vgl.algo in order to avoid this error from pybind11:

Traceback (most recent call last):
  File scripts/estimate_pose_example.py, line 36, in <module>
    pose = pix2face_estimation.camera_estimation.estimate_head_pose(img, pix2face_net, cuda_device)
  File /pix2face/python/pix2face_estimation/camera_estimation.py, line 19, in estimate_head_pose
    return extract_head_pose(estimate_camera(image, pix2face_net, cuda_device=cuda_device))
  File /pix2face/python/pix2face_estimation/camera_estimation.py, line 14, in extract_head_pose
    yaw, pitch, roll = decompose_camera_rotation(camera_params.rotation.as_matrix(), pitch_offset=-7)
TypeError: Unable to convert function return value to a Python type! The signature was
	(arg0: face3d.perspective_camera_parameters) -> vgl_rotation_3d<double>

python/pix2face_estimation/camera_estimation.py

@@ -1,5 +1,6 @@
 import face3d
 import pix2face.test
+import vxl.vgl.algo
 from .camera_decomposition import decompose_camera_rotation