Cache HTML suggestions / improve suggestion loading performance

[benbasson]

We are currently rebuilding the HTML for the suggestions list every time it's updated, which means (at minimum):

• sorting the list
• creating the HTML for every suggestion
• binding the event handlers for every suggestion
• dealing with hierarchy / existing selected tags

It seems like there are some decent performance gains to be had here - we could definitely look at at least caching the objects in memory so that we can re-insert them to the DOM faster. Another option is always leaving all suggestions in the DOM, but manipulating which are shown / not shown / not selectable.