(core) Show usage banners in doc menu of free team sites

Summary:
Also fixes a minor CSS regression in UserManager where the
link to add a team member wasn't shown on a separate row.

Test Plan: Browser tests.

Reviewers: jarek

Reviewed By: jarek

Differential Revision: https://phab.getgrist.com/D3444

app/common/roles.ts

@@ -1,3 +1,5 @@
+import {Organization} from 'app/common/UserAPI';
+
 export const OWNER  = 'owners';
 export const EDITOR = 'editors';
 export const VIEWER = 'viewers';
@@ -39,6 +41,15 @@ export function canView(role: string|null): boolean {
   return role !== null;
 }
 
+export function isOwner(resource: {access: Role}|null): resource is {access: Role} {
+  return resource?.access === OWNER;
+}
+
+export function canUpgradeOrg(org: Organization|null): org is Organization {
+  // TODO: Need to consider billing managers and support user.
+  return isOwner(org);
+}
+
 // Returns true if the role string is a valid role or null.
 export function isValidRole(role: string|null): role is Role|null {
   return (roleOrder as Array<string|null>).includes(role);