Description: Set the initial task button text (and icon) correctly
 Detailed explanation:
 .
 When a window shows up, the signal `KWindowSystem::stackingOrderChanged` is emitted *before* `KWindowSystem::windowAdded`. The former signal is connected to the function `LXQtTaskBar::refreshTaskList()`, which calls the functions `LXQtTaskBar::addWindow()` and `LXQtTaskBar::removeWindow()` to add and remove monitored windows.
 .
 Connecting `LXQtTaskBar::refreshTaskList()` to the signal `KWindowSystem::stackingOrderChanged` not only is redundant but also causes a problem:
 .
 (1) It's redundant because the job of adding *new* windows should be done by `LXQtTaskBar::onWindowAdded()` connected to the signal `KWindowSystem::windowAdded`. However, with the current code, `LXQtTaskBar::addWindow()` is never called by that function because the new window is already added through `KWindowSystem::stackingOrderChanged`. Similarly, `LXQtTaskBar::onWindowRemoved()` should be responsible for removing windows by being connected to the signal `KWindowSystem::windowRemoved`.
 .
 (2) More importantly, as the window name can change in the short interval between the emissions of `KWindowSystem::stackingOrderChanged` and `KWindowSystem::windowAdded`, the corresponding taskbar button may get a wrong text. The reason is that the signal `WindowSystem::windowChanged` announces changes only starting from the emission of `KWindowSystem::windowAdded`. (Theoretically, the initial icon might also be wrong but that's rarer).
 .
 Here, the connection to `KWindowSystem::stackingOrderChanged` is removed, so that the initial task button text/icon is set correctly. In this way, several useless calls to `LXQtTaskBar::refreshTaskList()` are also prevented when a window is shown/closed or focused/unfocused.
Author: Tsu Jan <tsujan2000@gmail.com>
Origin: backport
Bug: https://github.com/lxde/lxqt/issues/1303
Applied-Upstream: commit:563d6bf
Last-Update: 2018-02-05
--- a/plugin-taskbar/lxqttaskbar.cpp
+++ b/plugin-taskbar/lxqttaskbar.cpp
@@ -93,7 +93,6 @@ LXQtTaskBar::LXQtTaskBar(ILXQtPanelPlugi
     connect(mSignalMapper, static_cast<void (QSignalMapper::*)(int)>(&QSignalMapper::mapped), this, &LXQtTaskBar::activateTask);
     QTimer::singleShot(0, this, &LXQtTaskBar::registerShortcuts);
 
-    connect(KWindowSystem::self(), SIGNAL(stackingOrderChanged()), SLOT(refreshTaskList()));
     connect(KWindowSystem::self(), static_cast<void (KWindowSystem::*)(WId, NET::Properties, NET::Properties2)>(&KWindowSystem::windowChanged)
             , this, &LXQtTaskBar::onWindowChanged);
     connect(KWindowSystem::self(), &KWindowSystem::windowAdded, this, &LXQtTaskBar::onWindowAdded);