no issue
- adds new router to the frontend for handling unsubscribe
- default template lives in `core/server/frontend/views/unsubscribe.hbs`
- `{{error}}` is present and contains the error message when unsubscribe fails
- `{{member}}` is present and contains the member email
- updated unsubscribe url to match the new format
refs #10790
- Moved /core/apps into core/frontend
- Moved /core/server/helpers to /core/frontend/helpers along with /core/server/services/themes
- Changed helper location in overrides
- Moved /core/server/services/routing to /core/frontend/services
- Moved /core/server/services/url to /core/frontend/services
- Moved /core/server/data/meta to /core/frontend/meta
- Moved /core/server/services/rss to /core/frontend/services
- Moved /core/server/data/xml to /core/frontend/services