feat: multitab and basic file saving

mainwindow.h

@@ -6,6 +6,9 @@
 
 class QLabel;
 class SciEdit;
+class TabWidget;
+class DocumentManager;
+
 class MainWindow : public KXmlGuiWindow
 {
     Q_OBJECT
@@ -14,13 +17,29 @@ public:
     explicit MainWindow(QWidget *parent = nullptr);
     ~MainWindow();
 
+private slots:
+    void newFile();
+    void openFile();
+    void saveFile();
+    void saveAsFile();
+    void closeFile();
+    void onCurrentTabChanged();
+    void onCurrentEditorChanged(SciEdit *editor);
+    void onDocumentModified(int docIndex, bool modified);
+
 private:
     void setupActions();
     void showSettings();
     void applyLexer(const QString & lexer);
+    void updateWindowTitle();
+    void updateStatusBar();
+    void updateActions();
 
-    SciEdit * m_editor;
-    QLabel * m_cursorPosStatusLabel;
+    DocumentManager *m_documentManager;
+    TabWidget *m_tabWidget;
+    QLabel *m_cursorPosStatusLabel;
+    QLabel *m_encodingStatusLabel;
+    QLabel *m_languageStatusLabel;
 };
 
 // plainly for KConfigDialog