If a user is already a delegate, don't display the form

Solves LiskArchive#946.

Initially I attempted a redirect to the root page here so the modal
wouldn’t load if the user is a delegate. Due to the way this dialog is
opened though, that caused the dialog to quickly animate onto the page,
then disappear after the redirect was triggered. This is a quick
compromise for the UX.

i18n/locales/de/common.json

@@ -175,6 +175,7 @@
   "You can vote for up to {{count}} delegates in total.": "Du kannst insgesamt für {{count}} Delegierte stimmen.",
   "You can vote for up to {{count}} delegates in total._plural": "Bis zu {{count}} Delegierte können insgesamt von einem Konto gewählt werden.",
   "You have not forged any blocks yet": "Du hast noch keine Blöcke geforged",
+  "You have already registered as a delegate.": "Du hast bereits als Delegierter registriert.",
   "You need to become a delegate to start forging. If you already registered to become a delegate, your registration hasn't been processed, yet.": "Um Blöcke forgen (erstellen) zu können, musst du Delegierter werden. Wenn du dich schon als Delegierter registriert hast, wurde deine Registrierung noch nicht verarbeitet.",
   "You've received {{value}} LSK.": "Du hast {{value}} LSK erhalten.",
   "Your transaction of {{amount}} LSK to {{recipientAddress}} was accepted and will be processed in a few seconds.": "Deine Transaktion von {{amount}} LSK zu {{recipientAddress}} wurde akzeptiert und wird in wenigen Sekunden verarbeitet.",

i18n/locales/en/common.json

@@ -183,6 +183,7 @@
   "You can select up to {{count}} delegates in one voting turn._plural": "You can select up to {{count}} delegates in one voting turn.",
   "You can vote for up to {{count}} delegates in total.": "You can vote for up to {{count}} delegates in total.",
   "You can vote for up to {{count}} delegates in total._plural": "You can vote for up to {{count}} delegates in total.",
+  "You have already registered as a delegate.": "You have already registered as a delegate.",
   "You have not forged any blocks yet": "You have not forged any blocks yet",
   "You need to become a delegate to start forging. If you already registered to become a delegate, your registration hasn't been processed, yet.": "You need to become a delegate to start forging. If you already registered to become a delegate, your registration hasn't been processed, yet.",
   "You've received {{value}} LSK.": "You've received {{value}} LSK.",

src/components/registerDelegate/registerDelegate.js

@@ -17,6 +17,7 @@ class RegisterDelegate extends React.Component {
       ...authStatePrefill(),
     };
   }
+
   componentDidMount() {
     const newState = {
       name: {
@@ -40,6 +41,16 @@ class RegisterDelegate extends React.Component {
   }
 
   render() {
+    if (this.props.account.isDelegate) {
+      return (
+        <div>
+          <InfoParagraph>
+            {this.props.t('You have already registered as a delegate.')}
+          </InfoParagraph>
+        </div>
+      );
+    }
+
     return (
       <div>
         <form onSubmit={this.register.bind(this)}>