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/helloworld/helloworldplugin.cpp

@@ -109,6 +109,7 @@ bool HelloWorldPlugin::initialize(const QStringList &arguments, QString *error_m
     // it will unregister itself from the plugin manager when it is deleted.
     Core::BaseMode *baseMode = new Core::BaseMode;
     baseMode->setId(QLatin1String("HelloWorld.HelloWorldMode"));
+    baseMode->setType(QLatin1String("HelloWorld.HelloWorldMode"));
     baseMode->setDisplayName(tr("Hello world!"));
     baseMode->setIcon(QIcon());
     baseMode->setPriority(0);