VDFGenerator has incorrect imports

[pc494]

To Reproduce Steps to reproduce the behavior:

from pyxem.generators.vdf_generator import VDFGenerator

Throws:

---------------------------------------------------------------------------
ImportError                               Traceback (most recent call last)
<ipython-input-28-996234032340> in <module>
----> 1 from pyxem.generators.vdf_generator import VDFGenerator

~/miniconda3/envs/miniconda-1/lib/python3.8/site-packages/pyxem/generators/vdf_generator.py in <module>
     22 from hyperspy.api import roi
     23 
---> 24 from pyxem.signals.vdf_image import VDFImage
     25 from pyxem.utils.vdf_utils import normalize_vdf
     26 from pyxem.signals import transfer_signal_axes, transfer_navigation_axes_to_signal_axes

~/miniconda3/envs/miniconda-1/lib/python3.8/site-packages/pyxem/signals/vdf_image.py in <module>
     23 from pyxem.utils.segment_utils import separate_watershed
     24 from pyxem.signals.diffraction_vectors import DiffractionVectors
---> 25 from pyxem.signals import transfer_signal_axes
     26 from pyxem.signals.segments import VDFSegment
     27 

ImportError: cannot import name 'transfer_signal_axes' from 'pyxem.signals' (/home/phillip/miniconda3/envs/miniconda-1/lib/python3.8/site-packages/pyxem/signals/__init__.py)

I think this is because vdf_image is an old code, and from pyxem.signals.vdf_image import VDFImage should be redirected to the correct place instead - hopefully that will resolve the issue.

[pc494]

Closed by #66