Refactor search into a stateful class

[srawlins]

Fixes #3272 by changing initialize into a stateful class. Really helps with readability, promotion, etc.

This PR has a few little changes as well:

• rename 3 distinct variables named input which each represent something totally different
• add support for pressing 'Escape' in the search box
• fix result collection on search.html page
• selectedElement was a nullable int, with null meaning "nothing is selected." I found a nullable hint very awkward to work with, seeing lots of expressions like selectedElement! - 1. I was able to make this a non-nullable int, with -1 meaning "nothing is selected," and some helper functions like an extension on int called isBlurred.

[keertip]

👍