Fixes #4972 Domain in spamfilter_user settings not punicode encoded

Start checks against local sites list for allowed reverse proxy forwards

First workflow for allow reverse proxy with different site names
for ispconfig panel.

TODO: Allow only for sites known to the system itself instead
of all or none.

- reduced duplicate code in dns remoting function

104.3 MB looks better to me then the current 104.3345 MB. (is that level of detail is desired then maybe we should force kB notation.)

Maybe 2 or even three decimals ... but not 4.