Update (create) elasticsearch autocomplete fn
Use elasticsearch mixin in api/views/topics.py
Fix top search bar's autocomplete functionality

1. jquery-ui 1.9 introduced some accessibility improvements, one of
which is adding a message about navigating search results just after the
search input. That message is supposed to be hidden, but we don't use
jquery-ui's CSS file. I hidded it myself.

2. Top search bar now searches all items, not just topics. A label is
prepended to each result displaying the type of the result.

3. lil stylistic changes