Enhancement: Implement Server-Sent Events (SSE) for file updates

We've implemented Server-Sent Events (SSE) to notify users in real-time about file changes.
Users now receive real-time UI updates when e.g. the last modification date or size of a file is updated.

https://github.com/owncloud/web/pull/10782
https://github.com/owncloud/web/issues/10779
