Connect using Hostname

#### Issue details
Hostname connection not supported through UDPCI / TCP

I've checked previous issues for any mention, I've tried on MP and I've had a google - I could have missed a discussion or maybe the feature is already implemented in some way..

Currently need to specify IP - more convenient to specify hostname, especially where the IP of the device may be changing. For example the hostname would be "raspberrypi" by default for a pi.

#### Version
current

No file or test is named in the issue. Start by tracing Mission Planner's existing UDPCI and TCP connection entry points and how they currently validate or resolve IP addresses. Done means a hostname such as "raspberrypi" can be supplied instead of an IP and the connection works as requested.

Written by the indexing model from the issue text.