Summary:
- Makes EE decide which ActivationPage to use
- Makes ProductUpgrades use core implementation if not activated
- Changes banners to proxy to core implementation if EE not activated
- [Fix] Enables new site creation in EE as in Core:
- Core enables people to freely create new team sites.
- Enterprise currently redirects to the pricing page.
- This enables enterprise to also create team sites, instead of
redirecting.
Test Plan: Manually test in EE, unit tests in Jenkins
Reviewers: paulfitz, jordigh
Reviewed By: paulfitz
Differential Revision: https://phab.getgrist.com/D4264
