Replace virtual isModified method with a getter/setter/notifier

We have lacked the setter and dedicated notifier before.

Change-Id: I58845a48259d260c5cc90ae94b173c79cddcfef9
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>

src/plugins/bineditor/bineditorplugin.cpp

@@ -320,12 +320,6 @@ public:
     }
 
 public:
-    bool isModified() const override
-    {
-        return isTemporary()/*e.g. memory view*/ ? false
-                                                 : m_widget->isModified();
-    }
-
     bool isFileReadOnly() const override {
         const FileName fn = filePath();
         if (fn.isEmpty())
@@ -391,7 +385,12 @@ public:
         connect(m_addressEdit, &QLineEdit::editingFinished,
                 this, &BinEditor::jumpToAddress);
         connect(widget, &BinEditorWidget::modificationChanged,
-                m_file, &IDocument::changed);
+                m_file, &IDocument::setModified);
+        connect(m_file, &IDocument::modificationChanged,
+                widget, &BinEditorWidget::setModified);
+
+        m_file->setModified(widget->isModified());
+
         updateCursorPosition(widget->cursorPosition());
     }