OwnCloudDriver: Support for ownCloud & Nextcloud

[scy]

This is using pyocclient to implement a driver for ownCloud & Nextcloud.

As both of these systems rather use file/directory semantics instead of container/blob ones, the driver behaves somewhat similar to LocalDriver: A container can be any (sub)directory (including "" for the top-level directory), a blob is a file. Uploading blobs with slashes in their name will cause the respective parent directories to be created. Also, some features (e.g. ACLs and CDN URLs) are not supported.

Multiple ways of access are supported:

• “Normal” login: endpoint="https://cloud.example.com/", user="AzureDiamond", password="hunter2"
• “Share link” folder: endpoint="https://cloud.example.com/s/XAPaqtjYbg5cJca", user=None (or user=""), optionally password="hunter2" if the share is using a password, else password=None

The code is basically working, but not yet complete. Open tasks:

• [ ] add tests
• [ ] improve error handling & robustness
• [ ] add docstrings
• [ ] add documentation

If you have any comments, suggestions or criticism, let me know :)