Fixes: #809
Previously it was possible through the GUI to enter an IP address:port into the “Proxy IP” configuration box. After the node was restarted the errant setting would prevent the node starting back up until manually removed from settings.json.
Prevent this with a simple check for “:” in the string. This is acceptable here in the GUI setting because we already fail on a hostname such as “http://x.x.x.x”, so it won’t cause false positives.