Channel details: re-add the Host column in "User List", but only fill

Channel details: re-add the Host column in "User List", but only fill
it when using UnrealIRCd 6.0.8+. In older versions one would have to
do 1 API call for each user in the list which is way too slow when the
webserver and IRC server are on different machines (eg: load time of
40 seconds for a 100 user channel).
In UnrealIRCd 6.0.8+ this information is included in the single
channel.get() when requested, so we only have to do 1 API call and
not 101.