[OPEN] Code cleanup for FindInFiles.js

There are no functional changes (although I _was_ tempted to make some...).

Clean-ups include:

* Add a module level var named `$searchResultsDiv` that is now used in several places throughout the code.
* Refactor the code that hides results into a new `_hideSearchResults()` function, and call this function when needed.
* Update the `htmlReady` callback to initialize `$searchResultsDiv` instead of initializing a couple local vars that were never used.