Revert "Trust self-signed certificates (issue #454)"

This reverts commit f5869b8f3eb022355621ebe56a6f254329e435aa.
The commit "fixed" the issue on older JREs, but broke another gateway
(t-mobile) on newer JREs. Since I don't have any better solution, and
t-zones certificate is clearly broken, I revert this and thus keep
t-zones non-functional for the moment.

Related to issue #454.
[CZ]t-zones gateway: disable and add link to bug report

This gateway is currently broken because of issue #454 and it doesn't
seem to get fix soon.
bump version to 1.6