Enhancement: Dropdown actions in FilesTable

Users can now access quick actions in a dropdown by clicking on
the three-dots button or right-clicking on rows in the files table.

We've also bumped the ownCloud Design System to version 8.3.0

https://github.com/owncloud/owncloud-design-system/releases/tag/v8.3.0
https://github.com/owncloud/web/issues/5102
https://github.com/owncloud/web/issues/5103
https://github.com/owncloud/web/pull/5551
https://github.com/owncloud/web/pull/5554
