Move requiredEmail validation from state.js to dialog.js . Tests fail.

Since validation is done earlier, invalid addresses are reported as with
renderError() instead of startAction("doError"). So the tests which
watch for doError are now failing (the frontend tests named
"resources/state: start with invalid requiredEmail - print error screen"
and "resources/state: start with empty requiredEmail - prints error
screen". I don't know how to make them watch for renderError() instead.

One upside of this patch is that @stomlinson told me the three-argument
to startAction("doError"..) in state.js was a bug, as it only accepts
two real arguments. Removing it is even easier than fixing it.