on changed outgoing port should include an isValid flag

If you look at the output going ports for when a values changes:
 - `valueChangedHandlerSingleSelect`
 - `valueChangedHandlerMultiSelectSelect`

the JavaScript is doing a little bit of work to find out if there are _any_ invalid values. The Elm already knows this and it should just tell the JavaScript. Probably by including it, in the outgoing port's data.