ShareDialog: Add support for multiple public link shares #5655

ShareDialog: Add support for multiple public link shares #5655

Starting from oC 10.0.0 having several public link shares with
different attributes for a path will be supported. This adds
functionality to create, edit and delete these public link shares.

The behavior is currently gated by server version, but should be
adapted to use a capability as soon as one is introduced, see
owncloud/core#27622.

The UI reduces to a single-share version when talking to older servers.

Testing scenarios:
* Link sharing is disabled (by capability, not by theme)
* Required passwords
* Required expiry
* Forbidden 'allow upload' for folders
* New and old servers