[TASK] Update Travis CI notification settings

Notify on Slack and IRC, remove email notification.

Resolves: #59838
Releases: 6.3, 6.2, 4.5
Change-Id: Ic4dacd5c7b6b4e6e2b8cfa92ae7976b666209747
Reviewed-on: https://review.typo3.org/31209
Reviewed-by: Nicole Cordes
Reviewed-by: Michael Stucki
Tested-by: Michael Stucki
[TASK] Improve travis notifications to channels

By default travis notifies on each build when
posting to channels (irc, slack)
We can reduce the number of notifications by only
posting successful builds when it previously failed.
Additionally encrypt the API token for posting to slack.

Releases: 6.3, 6.2, 6.1, 6.0, 4.7, 4.5
Change-Id: I882d34903c972201454e6cc5b9041393e3bd3661
Reviewed-on: https://review.typo3.org/31226
Reviewed-by: Helmut Hummel
Tested-by: Helmut Hummel