feat(sidebar): provide public API to register a sidebar tab

[susnux]

This replaces the legacy OCA.Files.Sidebar. It also allows to define the order of the tab to prevent different order depending on the localized name like with the legacy tabs.

We probably need to support both in the files app for at least one version as we too short on the feature freeze - but at least this allows to properly use the Node API from this library inside tabs - instead of the old FileInfo model.

[skjnldsv]

• use web components as we do for workflowengine and files_sharing?

This. Incoming Viewer app is also using web components

[susnux]

@skjnldsv thank you for confirmation! :)