No way to add island's external IP

**Describe the bug**
At this moment there is no way to add external ip for the island. This means that if island is on Wi-fi and our target is outside the wireless network, island will be able to exploit it, but monkey won't connect back.

**To Reproduce**
Steps to reproduce the behavior:
1. Start island in a private network
2. Exploit host outside of LAN
3. Exploiting monkey passes local IP to the host, but due to NAT that IP is invalid.
4. Exploited host can't connect back.
**Expected behavior**
Monkey could detect when it's inside a private network and the host is outside, get it's external IP and pass it instead of internal
OR
We support multiple servers in command line. In config user can manually type in external ip that will always be passed as a backup IP to monkey command line