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/mercurial/mercurialplugin.cpp

@@ -593,7 +593,8 @@ void MercurialPlugin::showCommitWidget(const QList<QPair<QString, QString> > &st
     }
 
     Core::IEditor *editor = core->editorManager()->openEditor(changeLog->fileName(),
-                                                              QLatin1String(Constants::COMMIT_ID));
+                                                              QLatin1String(Constants::COMMIT_ID),
+                                                              Core::EditorManager::ModeSwitch);
     if (!editor) {
         outputWindow->appendError(tr("Unable to create an editor for the commit."));
         return;