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/vcsbase/vcsbaseoutputwindow.cpp

@@ -174,7 +174,7 @@ void OutputWindowPlainTextEdit::contextMenuEvent(QContextMenuEvent *event)
         }
         if (action == openAction) {
             const QString fileName = action->data().toString();
-            Core::EditorManager::instance()->openEditor(fileName);
+            Core::EditorManager::instance()->openEditor(fileName, QString(), Core::EditorManager::ModeSwitch);
         }
     }
     delete menu;