currentAndNext.js needs better messagebox support

[michael-grace]

the code enabling/disabling the messagebox does it on different parameters from the version in the view
the Go code does it based on !(jbox || offair), the js does it based on whether there's a timeslot
the js should do it the way the model and view decide this, and we could probably remove it from the go code, as the js updates it when the page loads anyway (i think)

also check if similar issue in radioplayer