(core) Adding latest version section to the admin panel.

Summary:
Update for the admin page to show the latest available version information.
- Latest version is read from docs.getgrist.com by default
- It sends basic information (installationId, deployment type, and version)
- Checks are done only on the page itself
- The actual request is routed through the API (to avoid CORS)

Test Plan: Added new test

Reviewers: paulfitz

Reviewed By: paulfitz

Subscribers: paulfitz

Differential Revision: https://phab.getgrist.com/D4238

app/client/lib/timeUtils.ts

@@ -4,8 +4,14 @@ import moment from 'moment';
  * Given a UTC Date ISO 8601 string (the doc updatedAt string), gives a reader-friendly
  * relative time to now - e.g. 'yesterday', '2 days ago'.
  */
-export function getTimeFromNow(utcDateISO: string): string {
-  const time = moment.utc(utcDateISO);
+export function getTimeFromNow(utcDateISO: string): string
+/**
+ * Given a unix timestamp (in milliseconds), gives a reader-friendly
+ * relative time to now - e.g. 'yesterday', '2 days ago'.
+ */
+export function getTimeFromNow(ms: number): string
+export function getTimeFromNow(isoOrTimestamp: string|number): string {
+  const time = moment.utc(isoOrTimestamp);
   const now = moment();
   const diff = now.diff(time, 's');
   if (diff < 0 && diff > -60) {