Dark GTK theme
Revert "Disable the whole system tray on Linux"

With Qt 5.3, QSystemTrayIcon no longer creates an extra
top level window on X11.

This reverts commit 9c580ece66fe1dda6285909b167544f22d3a556b.
Fix TextBrowser::onAnchorClicked()
Tree: restore the mechanism for highlighting network items
Refactor TreeHeader out of TreeDelegate
Refactor TreeBadge out of TreeDelegate
Refactor TreeSpinner out of TreeItem
Themable TreeIndicator
Remember last highlight
Minimalistic formatting for numeric messages
MessageFormatter: use IrcInviteMessage::isReply()
Require libcommuni 3.3
Fix alert for visible documents but inactive window
OSX: fix the top margin of the user listview
Merged events: distinguish abrupt disconnection from quit
Tree: remember last seen messages for badges

Don't increase badge numbers for already seen messages (bouncer users).
Tweak the tree indicator
Tweak the tree indicator on Windows
Fix last seen messages stamp for tree badges
Reset connection error highlight upon successful connection