Fix live notes refresh in relative URL deployments

### What does this MR do?

This MR fixes URLs used for refreshing notes--the relative_url prefix was appended twice

### Why was this MR needed?

In case of `relative_url` installation, opening a page which does refresh notes (i.e. merge request), the page generates lots of 404 errors in the browser console. It turns out that the relative_url is prepended to the link twice.

Supersedes !233

See merge request !1048