no issue
- The modal only appears when the user hits a limitation trying to activate a custom theme not part of the allowlist (if the custom theme allowlist is configured)
- Changed the upgrade button to green to match the design
refs https://github.com/TryGhost/Team/issues/480
- switched marketplace themes to a selection of Ghost's own free themes
- added install and preview buttons for all
- show theme screenshot in the install modal if it's a known theme