IrcBufferModel: don't create "*" buffers

Take a step back. b53775b changed things so that no buffers would be
created when the name contained an asterisk. This does not play nice
with the default ZNC prefix.
Merge branch '3.2'
Declare IrcCommandPrivate in irccommand_p.h
Add static IrcCommandPrivate::get()
Add IrcCommand::connection
Add IrcJoinMessage::account and realName (extended-join)
Add a dedicated message type for account-notify
Add a dedicated message type for away-notify
IrcMessageBuilder: add support for IrcAwayMessage ie. RPL_(UN|NOW)AWAY
IrcChannelPrivate: cleanup useless references
Add IrcUserModelPrivate::updateUser()
IrcUserModel: emit dataChanged() for away & servop status
Follow coding style
IrcBufferModel: process away-notify messages
Add IrcChannel::who() slot for convenience
Fix linking order for static libs
Let disable both icu & uchardet
Travis: use build matrix for choosing between Qt 5 and 4