New teal color for announcement alerts

## Narrative
By request [https://trello.com/c/nB85DwsB/494-make-announcement-hyperlink-more-visible] the announcement alert is now teal instead of lpblue

## Verification steps
1. Fire up Rizzo
2. Visit http://localhost:8080/styleguide/ui-components/alerts
3. Verify that the announcement type alert has the teal background color