Hide cert install instructions until we know they're needed

This makes the UX a lot smoother and avoids jumping between states

Author: pimterry

src/cert-check-server.ts

@@ -32,6 +32,7 @@ function ensureCertificateIsInstalled() {
                 // Start trying to prompt the user to install the cert
                 if (!installingCert) {
                     installingCert = true;
+                    document.body.className = 'show-content';
                     const iframe = document.createElement('iframe');
                     iframe.src = downloadUrl;
                     document.body.appendChild(iframe);
@@ -71,6 +72,10 @@ export class CertCheckServer {
                         font-family: Lato, Arial;
                     }
 
+                    body:not(.show-content) > * {
+                        display: none;
+                    }
+
                     h1 {
                         font-size: 36pt;
                     }