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... :/

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

java/google/registry/ui/externs/json.js

@@ -68,6 +68,7 @@ registry.json.Response.prototype.results;
 // XXX: Might not need undefineds here.
 /**
  * @typedef {{
+ *   allowedTlds: !Array<string>,
  *   clientIdentifier: string,
  *   clientCertificate: string?,
  *   clientCertificateHash: string?,