Clear highlights and Find selection color when modal bar closes

This is my second attempt at #5239. First attempt is #5240.

Read this comment: https://github.com/adobe/brackets/pull/5240#issuecomment-24966396

@njx This is just a simple "close" event (first bullet from comment above). All it does is clear highlights and reset selection color. Worst case is that it's called twice.

Regarding your second bullet, I don't see the case that needs to fixed. Everything seems to work correctly with this code. Please let me know.