Infelicities in plugin search UI

[ToxicFrog]

Three minor issues I encountered when using this the other day:

• there is no indicator that the search has been accepted; when you type something in, there is a delay and then the sidebar updates to show the results
• ...unless there are no results, in which case nothing happens, so there's no way to distinguish between "search still running" and "search completed and returned the empty set"
• if you don't realize the above and think you need to press enter to search, it reloads the same page with your search cleared and ? appended to the URL

Search still works, but this isn't great UX.

Suggested mitigations:

• display a visible indicator when the search is running
• display "no results" or similar if the search finds nothing
• make enter in the search box a no-op