EditorManager: Change openEditor/activateEditor to not do mode switching

Also introduce a indirection, modes have now types, edit and debug have
the same type, and editors do have a prefered type of modes instead of a
prefered mode.

That fixes the bug that if the prefered qml editing mode was set to
design, then in switching between qml editors would
- in Edit Mode: stay in edit mode
- in Debug Mode: switch to debug mode

src/plugins/coreplugin/editortoolbar.cpp

@@ -256,12 +256,12 @@ void EditorToolBar::changeActiveEditor(int row)
 
     if (editor) {
         if (editor != em->currentEditor())
-            em->activateEditor(editor, EditorManager::NoModeSwitch);
+            em->activateEditor(editor);
     } else {
         //em->activateEditor(model->index(index, 0), this);
         QString fileName = model->data(modelIndex, Qt::UserRole + 1).toString();
         QByteArray kind = model->data(modelIndex, Qt::UserRole + 2).toByteArray();
-        editor = em->openEditor(fileName, kind, EditorManager::NoModeSwitch);
+        editor = em->openEditor(fileName, kind);
     }
     if (editor) {
         m_editorList->setCurrentIndex(m_editorsListModel->indexOf(editor).row());