Suggestions endpoint: make RTL aware
Use new-style AJAX callbacks in remote_filter
remote_filter: empty response is OK in callback

The empty response will cause at.js to hide the suggestions panel, yay.
Revert "Suggestions: fix tests"

This reverts commit 063a01bad74f63f05b773d1f2700c46846f5b922.
Tweak search_wildcard for better result matching