Canvas validation enhancements

Right now, we have a lot of users hitting 3 main errors in creating a form: Each branch should end in a terminal node - this error is too generic and doesn't point them out which node is orfan. We need to highlight in red the node(s) with errors Ending node can wrongly be set as email/meta/sms. We need to only allow the ending node to be text and/or redirect. For this validation, we need a UI that shows up with a visual showing that email/meta/sms should be place in between the last node and thank you/redirect Maximum call stack error: if you create a circular reference in your form, it lets you save it (it shouldn't), but form rendering throws an error saying maximum call stack reached. We need verify this at publish, throw an error message and (if possible), highlight the node with circular reference.