Add expiration date support for shared links

[TRoc81]

Added support for expiration date on shared links

[onyx-and-iris]

I might suggest snake casing the two words expire_date as they are camel cased in the official API:

https://doc.owncloud.com/server/next/developer_manual/core/apis/ocs-share-api.html#create-a-new-share

[onyx-and-iris]

Good update, it would be worth adding expiration to the returned ShareInfo object as well.

Here's an example implementation, perhaps it can be improved upon:

                "name": data_el.find("name").text,
                "expiration": int(
                    round(
                        datetime.datetime.strptime(
                            data_el.find("expiration").text, "%Y-%m-%d %H:%M:%S"
                        ).timestamp()
                    )
                ),

It would also be worth expanding the test case.