Focus the first invalid field

This adjusts the submission step to focus the first invalid field and redisplay
validation. This also rearranges the older style field error handling on
registration which is slated for removal once we convert all fields to the new
style.

src/components/views/elements/Field.js

@@ -86,6 +86,10 @@ export default class Field extends React.PureComponent {
         }
     };
 
+    focus() {
+        this.input.focus();
+    }
+
     validate({ value, focused }) {
         if (!this.props.onValidate) {
             return;
@@ -107,6 +111,7 @@ export default class Field extends React.PureComponent {
 
         // Set some defaults for the <input> element
         inputProps.type = inputProps.type || "text";
+        inputProps.ref = input => this.input = input;
         inputProps.placeholder = inputProps.placeholder || inputProps.label;
 
         inputProps.onFocus = this.onFocus;