(core) Polishing upgrade plan UI

Summary:
- Update nudge boxes content and collapsing on personal and free team site
- New confirmation after upgrading from a free team site
- Refactoring ProductUpgrade code, splitting plans / modals and nudges

Test Plan: Manual and updated tests

Reviewers: georgegevoian

Reviewed By: georgegevoian

Differential Revision: https://phab.getgrist.com/D3481

app/common/Prefs.ts

@@ -38,9 +38,6 @@ export interface UserOrgPrefs extends Prefs {
 
   // List of document IDs where the user has seen and dismissed the document tour.
   seenDocTours?: string[];
-
-  // Whether the user seen the nudge to upgrade to Free Team Site and dismissed it.
-  seenFreeTeamUpgradeNudge?: boolean;
 }
 
 export type OrgPrefs = Prefs;