lookandfeel: Allow setting the plasmashell preferred Shell

kcms/lookandfeel/kcm.cpp

@@ -387,6 +387,12 @@ void KCMLookandFeel::save()
             setWindowPlacement(cg.readEntry("Placement", QStringLiteral("Smart")));
         }
 
+        if (m_applyShellPackage) {
+            cg = KConfigGroup(conf, "plasmashellrc");
+            cg = KConfigGroup(&cg, "Shell");
+            setShellPackage(cg.readEntry("ShellPackage", QString()));
+        }
+
         if (m_applyWindowDecoration) {
             cg = KConfigGroup(conf, "kwinrc");
             cg = KConfigGroup(&cg, "org.kde.kdecoration2");
@@ -750,6 +756,11 @@ void KCMLookandFeel::setWindowPlacement(const QString &value)
     writeNewDefaults(QStringLiteral("kwinrc"), QStringLiteral("Windows"), QStringLiteral("Placement"), value);
 }
 
+void KCMLookandFeel::setShellPackage(const QString &value)
+{
+    writeNewDefaults(QStringLiteral("plasmashellrc"), QStringLiteral("Shell"), QStringLiteral("ShellPackage"), value);
+}
+
 void KCMLookandFeel::setWindowDecoration(const QString &library, const QString &theme)
 {
     if (library.isEmpty()) {

kcms/lookandfeel/kcm.h

@@ -74,6 +74,7 @@ public:
     void setDesktopSwitcher(const QString &theme);
     void setWindowDecoration(const QString &library, const QString &theme);
     void setWindowPlacement(const QString &value);
+    void setShellPackage(const QString &name);
 
     Q_INVOKABLE void knsEntryChanged(KNSCore::EntryWrapper *wrapper);
     Q_INVOKABLE void reloadConfig()
@@ -134,6 +135,7 @@ private:
     bool m_applyWindowSwitcher : 1;
     bool m_applyDesktopSwitcher : 1;
     bool m_applyWindowPlacement : 1 = true;
+    bool m_applyShellPackage : 1 = true;
     bool m_resetDefaultLayout : 1;
     bool m_applyWindowDecoration : 1;
 };