Move remaining code to app module

There's still some stuff that could potentially go elsewhere but I think it's enough for now.

src/app/trayicon_sni.cpp

@@ -0,0 +1,32 @@
+// SPDX-FileCopyrightText: 2021 Aleix Pol Gonzalez <aleixpol@kde.org>
+// SPDX-License-Identifier: GPL-3.0-only
+
+#include "trayicon_sni.h"
+#include <KWindowSystem>
+
+#include "windowcontroller.h"
+
+using namespace Qt::StringLiterals;
+
+TrayIcon::TrayIcon(QObject *parent)
+    : KStatusNotifierItem(parent)
+{
+    setCategory(KStatusNotifierItem::ItemCategory::Communications);
+    setIconByName(u"org.kde.neochat.tray"_s);
+
+    connect(&WindowController::instance(), &WindowController::windowChanged, this, [this] {
+        setAssociatedWindow(WindowController::instance().window());
+    });
+}
+
+void TrayIcon::show()
+{
+    setStatus(Active);
+}
+
+void TrayIcon::hide()
+{
+    setStatus(Passive);
+}
+
+#include "moc_trayicon_sni.cpp"