Quick search should provide feedback to user if no matches are found

As someone working with a large (and often slow) CiviCRM instance daily, the 'quick search' can become quite frustrating, as there is no way to tell if a search has completed with no results, or is still happening. This has led to most users in my organisation immediately hitting return, which negates the auto-complete functionality.

The quick search widget should provide some feedback to indicate that a search has completed with no results.

I will be working to have a suitable pull request soon.