Add "Admin" tab to the registrar console

This tab will set the "allowedTlds", but might have other functionality in the
future.

It is based on (branches from) the security-settings tab, because I'm copying the functionality of the "whitelisted IPs" to the "allowed TLDs": they are both lists of "arbitrary" strings that you can remove from and add to.

There are a lot of moving parts in this CL, because of how all the different elements need to interact, and how intertwined they are (for example, we need to disable the admin-settings view for non admins both in the soy and in the JS code)

It's really time to refactor the console given all we've learned... :/

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=220373443

java/google/registry/ui/soy/registrar/Console.soy

@@ -24,6 +24,7 @@
   {@param xsrfToken: string} /** Security token. */
   {@param clientId: string} /** Registrar client identifier. */
   {@param allClientIds: list<string>} /** All registrar client identifiers for the user. */
+  {@param isAdmin: bool}
   {@param username: string} /** Arbitrary username to display. */
   {@param logoutUrl: string} /** Generated URL for logging out of Google. */
   {@param productName: string} /** Name to display for this software product. */
@@ -63,6 +64,7 @@
     <script>
       registry.registrar.main({$xsrfToken},
                               {$clientId},
+                              {if $isAdmin}true{else}false{/if},
                               {$productName},
                               {$integrationEmail},
                               {$supportEmail},
@@ -78,6 +80,7 @@
 {template .navbar_ visibility="private"}
   {@param clientId: string} /** Registrar client identifier. */
   {@param allClientIds: list<string>}
+  {@param isAdmin: bool}
 
   <div id="reg-nav" class="{css('kd-content-sidebar')}">
     <form>
@@ -105,6 +108,10 @@
             <a href="#security-settings">Security</a>
           <li>
             <a href="#contact-settings">Contact</a>
+          {if $isAdmin}
+            <li>
+              <a href="#admin-settings">Admin</a>
+          {/if}
         </ul>
       <li>
         <a href="#contact-us">Contact us</a>