(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/ui2018/checkbox.ts

@@ -16,7 +16,7 @@
  */
 
 import {testId, theme} from 'app/client/ui2018/cssVars';
-import {Computed, dom, DomArg, DomContents, Observable, styled} from 'grainjs';
+import {Computed, dom, DomArg, DomContents, DomElementArg, Observable, styled} from 'grainjs';
 
 export const cssLabel = styled('label', `
   position: relative;
@@ -194,6 +194,19 @@ export const cssRadioCheckboxOptions = styled('div', `
   gap: 10px;
 `);
 
+export function toggle(value: Observable<boolean|null>, ...domArgs: DomElementArg[]): DomContents {
+  return dom('div.widget_switch',
+    (elem) => elem.style.setProperty('--grist-actual-cell-color', theme.controlFg.toString()),
+    dom.hide((use) => use(value) === null),
+    dom.cls('switch_on', (use) => use(value) || false),
+    dom.cls('switch_transition', true),
+    dom.on('click', () => value.set(!value.get())),
+    dom('div.switch_slider'),
+    dom('div.switch_circle'),
+    ...domArgs
+  );
+}
+
 // We need to reset top and left of ::before element, as it is wrongly set
 // on the inline checkbox.
 // To simulate radio button behavior, we will block user input after option is selected, because