(core) show package.json version when hovering on Grist icon in grist-core

Summary:
This makes the version shown when hovering on the Grist icon equal
the version set in package.json, for a grist-core build. Previously
the number shown was a hard-coded placeholder.

The Grist SaaS build has some build machinery dealing with the
version number that should be unaffected by this change for now.

Test Plan: tested manually with build_core.sh

Reviewers: jarek

Reviewed By: jarek

Differential Revision: https://phab.getgrist.com/D3659

app/client/ui/AppHeader.ts

@@ -39,8 +39,12 @@ export class AppHeader extends Disposable {
     return cssAppHeader(
       cssAppHeader.cls('-widelogo', productFlavor.wideLogo || false),
       // Show version when hovering over the application icon.
+      // Include gitcommit when known. Cast version.gitcommit since, depending
+      // on how Grist is compiled, tsc may believe it to be a constant and
+      // believe that testing it is unnecessary.
       cssAppLogo(
-        {title: `Ver ${version.version} (${version.gitcommit})`},
+        {title: `Version ${version.version}` +
+          ((version.gitcommit as string) !== 'unknown' ? ` (${version.gitcommit})` : '')},
         urlState().setLinkUrl({}),
         testId('dm-logo')
       ),