Optional setTimeout on sticky nav

On pages running Optimizely A/B tests, the sticky nav behaves undesirably in the event that the A/B test is changing content that effects the top offset of the sticky nav (which is calculated before Optimizely kicks in).

Calculating the offset inside `setTimeout(fn, 0)` solves the issue - this pull request adds this as an `optimizelyTimeout` option that can be switched on for individual sticky navs (rather than changing it site-wide purely for Optimizely's sake) and also switches this on for the sticky nav on /basic for the purposes of an existing A/B test.