Follow redirects when adding webdav mount (#1582)

* Follow redirects when adding webdav mount

Signed-off-by: Sunik Kupfer <kupfer@bitfire.at>

* Update dav4jvm version

* Remove unused null

* Fix tests

* Add Kdoc

* Add Kdoc

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Signed-off-by: Sunik Kupfer <kupfer@bitfire.at>
Co-authored-by: Ricki Hirner <hirner@bitfire.at>