closes #434, #408 - added $event to onValidationError and call preventDefault when onValidateBeforeSubmit is true

We can't prevent the submit after waiting for async validation, so we just prevent it before calling any validation and let the user
manually submit the form in the `onSubmit` handler, if it validates.

Author: zoul0813

src/fields/core/fieldSubmit.vue

@@ -12,10 +12,13 @@
 		methods: {
 			onClick($event) {
 				if (this.schema.validateBeforeSubmit === true) {
+					// prevent a <form /> from having it's submit event triggered
+					// when we have to validate data first
+					$event.preventDefault();
 					let errors = this.$parent.validate();
 					let handleErrors = (errors) => {
 						if(!isEmpty(errors) && isFunction(this.schema.onValidationError)) {
-							this.schema.onValidationError(this.model, this.schema, errors);
+							this.schema.onValidationError(this.model, this.schema, errors, $event);
 						} else if (isFunction(this.schema.onSubmit)) {
 							this.schema.onSubmit(this.model, this.schema, $event);
 						}
@@ -27,6 +30,8 @@
 						handleErrors(errors);
 					}
 				} else if (isFunction(this.schema.onSubmit)) {
+					// if we aren't validating, just pass the onSubmit handler the $event
+					// so it can be handled there
 					this.schema.onSubmit(this.model, this.schema, $event);
 				}
 			}