Improve filter performance.

Filtering performed rather poor for the first query when more than 1000 options. The bottleneck were these lines - `$(element).show().removeClass("filter-hidden");`, `$(element).hide().addClass("filter-hidden");`. So I optimized them by adding `display: none` to class `filter-hidden`. Also most of the condition operations were moved out of the loop, because they didn't depend on option's value.