Added an optional no-suggestions notice when no matching results

This feature aims to improve user experience and plugin's responsiveness
by providing instant feedback for empty searches.

A customizable notice label is appended to the suggestions container.

Here is a quick view:
https://www.evernote.com/shard/s260/sh/a3db260a-0bd2-40d4-a12c-1a728940f68f/5a43cbbfb7775e87b375790e94f15949/deep/0/DevBridge%20Autocomplete%20Demo.png%20(1656%C3%97842).png