Improve performance of large option lists

[StefanH]

I've noticed large option lists in selects cause the browser to timeout when rendering selectize.
Detaching the input, then detaching the children from it,
then re-attaching the input dramatically improves performance.

[joallard]

Thanks for the patch.

So I've tried this out with a new example in the performance demos and a profiler open. I see no difference with a select with 12k options. Firefox is 5.5s -> 6s and Chrome 51 2.5s -> 2.5s

Would you try branch pr-1105 at examples/performance.html, 2nd example, and figure out if there's a way to test this? Thanks!

[github-actions]

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