Add mainnet beta upgrade announcement

explorer/src/components/Banner.tsx

@@ -20,6 +20,11 @@ const announcements = new Map<Cluster, Announcement>();
 //   start: new Date("August 1, 2020 00:00:00 GMT+0:00"),
 //   end: new Date("August 3, 2020 00:00:00 GMT+0:00"),
 // });
+announcements.set(Cluster.MainnetBeta, {
+  message:
+    "Mainnet Beta upgrade over the weekend of August 1, 2020. " +
+    "TRANSACTIONS DISABLED DURING THE UPGRADE",
+});
 
 export default function Banner() {
   const cluster = useCluster().cluster;
@@ -31,14 +36,10 @@ export default function Banner() {
   if (end && now > end) return null;
   if (start && now < start) return null;
 
-  return (
-    <div className="bg-danger text-white">
-      <div className="container">
-        <div className="d-flex flex-column align-items-center justify-content-center text-center py-3">
-          <h3 className="mb-3">
-            <span className="fe fe-alert-circle mr-2"></span>
-            {message}
-          </h3>
+  let timeframe;
+  if (estimate || start || end) {
+    timeframe = (
+      <div>
         <hr className="text-gray-500 w-100 mt-0 mb-3 opacity-50" />
         {estimate && (
           <h5 className="font-sm text-gray-200">
@@ -59,6 +60,19 @@ export default function Banner() {
           </h5>
         )}
       </div>
+    );
+  }
+
+  return (
+    <div className="bg-danger text-white">
+      <div className="container">
+        <div className="d-flex flex-column align-items-center justify-content-center text-center py-3">
+          <h3 className="mb-3">
+            <span className="fe fe-alert-circle mr-2"></span>
+            {message}
+          </h3>
+          {timeframe}
+        </div>
       </div>
     </div>
   );