Confconsole: hostname plugin improvements; zeroconf plugin

[JedMeister]

There have been some great Confconsole Hostname plugin (Advanced >> System Settings >> Hostname) improvement suggestions from Aaron on the forums. Plus some other related ideas. Namely:

• pre-configure hostname in interfaces file (so it's updated when the Confconsole plugin is run, currently it will update it, but must first be manually set in the interfaces file)
• display hostname before/when changing the hostname
• ensure that the interfaces file includes the hostname by default (it already updates it if set)
• zeroconf install/config plugin

[JedMeister]

The hostname stuff should be in v18.0. The other suggestions are still outstanding.