(core) Disabling plugin import sources menu options when import is disabled

Summary: Disabling import sources from add menu when a user is not allowed to import.

Test Plan: browser tests

Reviewers: paulfitz

Reviewed By: paulfitz

Subscribers: paulfitz

Differential Revision: https://phab.getgrist.com/D2970

app/client/ui/HomeLeftPane.ts

@@ -176,6 +176,7 @@ function addMenu(home: HomeModel, creating: Observable<boolean>): DomElementArg[
       menuItem(() => importFromPluginAndOpen(home, source),
         menuIcon('Import'),
         source.importSource.label,
+        dom.cls('disabled', !home.newDocWorkspace.get()),
         testId(`dm-import-plugin`)
       ))
     ])),