Add mercury editor to terms and privacy pages

- Terms of use page can be edited by admin (if editing allowed in this particular marketplace)
- Privacy policy page can be edited by admin (if editing allowed in this particular marketplace)
- Simplified the process of adding mercury editor to new content pages 
- Renamed how to use page column in community customizations for consistency
- Removed mention about mobile app from default welcome email
- Added possibility to add storefront label to name in profile (it is now shown if there is corresponding string in community customization)
- [ ] Tests passing cucumber features/communities/user_views_terms.feature:15
- [ ] Add new db row
- [ ] Terms title twice
- [x] Service name genetive (fi)