Fix the position of the banners

Fixes bugs with the first position in parallax banners.

https://trello.com/c/Ctzkwi65/326-parralax-headers-and-weekly-photos-often-broken-in-safari
https://trello.com/c/TfAmgTAx/341-banner-in-interests-not-displaying-correctly-again


Why do we need to wait for the onload event? What is it that you need to be ready before initialising?