extend tests, fix issues with new Ip methods

Make is_ssl and baseurl use proper proxy checks

This should not only address #4455 but also ensures that the related
headers are only used when they come from a trusted reverse proxy chain.

Fix Ip tests

We no longer use the old regexp based config, so the tests failed.

rename trustedproxy option to trustedproxies

We use a new format (array instead of regex) and need a sure way to
recognize it. Zebra's approach would not have survived the editing via
config manager

rename trustedproxy option to trustedproxies

We use a new format (array instead of regex) and need a sure way to
recognize it. Zebra's approach would not have survived the editing via
config manager.
As a side effect this also introduces a new languange string, which is
good because the old one did no longer apply.

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some small cleanups in Ip class

most importantly do not crash on invalid config

Move IP functions into a class