[Feature Request] Apply rule if pattern does not match

I want to create a rule to block all but localhost connections. [Rules editor](https://github.com/evilsocket/opensnitch/wiki/Rules-editor) tells me to use negated character classes:
```
[x] Action: deny
[x] To this destination IP: [^:127.0.0.1:]
```

AFAIK, there are no custom character classes in regex, and the above pattern is equivalent to `[^0127.:]`, i.e. it's gonna match `172.21.0.17` and similar addresses besides `127.0.0.1`.

Since negative lookarounds are not supported, can you please add an ability to invert a match (like `grep -v`)?