Improved chnroutes to also easily delete rules

Doesn't change previous behaviour, by using sane
defaults so doesn't break backwards compatiblity
with people already using the scripts.

You can simple delete added rules with
./chnroutes.sh down

And adding with either `chnroutes.sh add` or just `chnroutes.sh`
Merge pull request #49 from samos123/chnroutes-improvement

Improved chnroutes to also easily delete rules
update client script

Only need to specify the VPN interface.