nextcloud support

Using the suggestion from Emanuele to use nextcloud through webdavs, downloads the needed files to temp folder (which is deleted on exit.

I think this will be more useable than the previous solution. Maybe you want it to be an optional setting which system to use.

You might want to do cosmetic changes, my code is not the nicest usually...

Maybe it makes more sense to keep the essnextcloud class somewhere else?

setup.py

@@ -4,7 +4,7 @@ from setuptools import setup, find_packages
 with open("README.rst") as readme_file:
     readme = readme_file.read()
 
-requirements = ["numpy", "h5py", "matplotlib"]
+requirements = ["numpy", "h5py", "matplotlib", "webdav3"]
 
 test_requirements = ["pytest", "pytest-cov", "responses", "pytest-mock"]