Summary:
- Remove the empty-folder icon
- Add an "Invite team members" button for owners on empty team sites
- Add a "Browse Templates" button for all other cases on empty sites
- Update intro text for team, including a link to Sprouts
- Update intro text for personal/anon.
- Include a Free/Pro tag for team sites (for now, only "Free")
- Add a "Manage Team" button for owners on home page of all team sites.
- Polished the UI of UserManager: add a transition for the background, and
delay the appearance of the spinner for fast loads.
Test Plan: Fixed up the HomeIntro tests; added test case for Manage Team button
Reviewers: georgegevoian
Reviewed By: georgegevoian
Differential Revision: https://phab.getgrist.com/D3459
