Unfriendly Auto-complete editing experience

[RabebOthmani]

With the new work done on Auto-complete , it now tried to complete on every key press not just the slash making the editing experience challenging. Feedback received from a user:" entering a query is now broken. for each character typed into the query box, a suggestion is fetch and that locks and hangs the UI. We cannot type a query anymore."

Also note that when fetching suggestions, the substring search is done while it should be a 'starts with'