Allow adding chromecast manually

[karel1980]

When the iot gateway and the chromecast are on a different network the mdns discovery wouldn't work. As a workaround it would be nice if you could add a chromecast manually.

[freaktechnik]

I'm not sure how the communication would work in the case where the mDNS discovery can't work. Unless it can still route to it internally, it's just that something blocks the mDNS packets.

[karel1980]

The setup is as follows: There is a router between the gateway and the chromecast; The gateway is on the internal network of the router and the chromecast is on the external network. (Giving guests access to the chromecast but not to the webthings gateway). I'll have a look if I can make the router allow mDNS packets to go to the external network.