Added o-date--ready class for conditional styling

@triblondon @AlbertoElias https://github.com/Financial-Times/o-date/issues/18

I can't get both local demos to build using `origami-build-tools demo --local`. It seems to always ignore each entry except for the last one in the array. I'm not sure if this is an OBT bug or the demo config is wrong (the correct format isn't documented in OBT) - could one of you take a look please.