Summary:
Adds an activation page to grist-ee that currently shows activation status.
Follow-up diffs will introduce additional functionality, such as the ability to
enter activation keys directly from the activation page.
Test Plan: No grist-ee tests (yet).
Reviewers: paulfitz
Reviewed By: paulfitz
Subscribers: dsagal, paulfitz
Differential Revision: https://phab.getgrist.com/D3582
