@ashfurrow => Use the RAC mapping to inline set 

Turns out there were a lot of issues around the RAC mapping. The worst being the compiler segfaulting. Trying to work around that eventually ended up turning JSONAble into a subclass instead. Downsides, as you know, are that we now have to cast straight away after a request.

This part of the mapping process is now tested :+1: 

The other aspect is that a SaleArtwork is now passed in to the popover. @1aurabrown - I'll note where I'm going from a model to changing view code using `RAC()`inline. It's not accurate ( as we get it in cents ) but I'll get around to that maybe in another commit or a new PR to show how to transform signal.
Not a practical issue, but any reason not to do `countElements(number)`?